| 1. |
- Allen, P. D., et al.
(författare)
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Low-frequency low-field magnetic susceptibility of ferritin and hemosiderin
- 2000
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Ingår i: Biochimica et Biophysica Acta - Molecular Basis of Disease. - 0925-4439 .- 1879-260X. ; 1500:2, s. 186-196
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Tidskriftsartikel (refereegranskat)abstract
- Low-frequency low-field magnetic susceptibility measurements were made on four samples of mammalian tissue iron oxide deposits. The samples comprised: (1) horse spleen ferritin; (') dugong liver hemosiderin; (3) thalassemic human spleen ferritin; and (4) crude thalassemic human spleen hemosiderin. These samples were chosen because Mossbauer spectroscopic measurements on the samples indicated that they exemplified the variation in magnetic and mineral structure found in mammalian tissue iron oxide deposits. The AC-magnetic susceptometry yielded information on the magnetization kinetics of the four samples indicating samples 1, 2, and 3 to be superparamagnetic with values of around 10(11) s(-1) for the preexponential frequency factor in the Neel-Arrhenius equation and values for characteristic magnetic anisotropy energy barriers in the range 250-400 K. Sample 4 was indicated to he paramagnetic at all temperatures above 1.3 K. The AC-magnetic susceptometry data also indicated a larger magnetic anisotropy energy distribution in the dugong liver sample compared with samples 1 and 3 in agreement with previous Mossbauer spectroscopic data on these samples. At temperatures below 200 K, samples 1-3 exhibited Curie-Weiss law behavior, indicating weak particle-particle interactions tending to favor antiparallel alignment of the particle magnetic moments. These interactions were strongest for the dugong liver hemosiderin. possibly reflecting the smaller separation between mineral particles in this sample. This is the first magnetic susceptometry study of hemosiderin iron deposits and demonstrates that the AC-magnetic susceptometry technique is a fast and informative method of studying such tissue iron oxide deposits.
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| 2. |
- Andersson, Richard L., et al.
(författare)
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Micromechanics of ultra-toughened electrospun PMMA/PEO fibres as revealed by in-situ tensile testing in an electron microscope
- 2014
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 4, s. 6335-
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Tidskriftsartikel (refereegranskat)abstract
- A missing cornerstone in the development of tough micro/nano fibre systems is an understanding of the fibre failure mechanisms, which stems from the limitation in observing the fracture of objects with dimensions one hundredth of the width of a hair strand. Tensile testing in the electron microscope is herein adopted to reveal the fracture behaviour of a novel type of toughened electrospun poly(methyl methacrylate)/poly(ethylene oxide) fibre mats for biomedical applications. These fibres showed a toughness more than two orders of magnitude greater than that of pristine PMMA fibres. The in-situ microscopy revealed that the toughness were not only dependent on the initial molecular alignment after spinning, but also on the polymer formulation that could promote further molecular orientation during the formation of micro/nano-necking. The true fibre strength was greater than 150 MPa, which was considerably higher than that of the unmodified PMMA (17 MPa). This necking phenomenon was prohibited by high aspect ratio cellulose nanocrystal fillers in the ultra-tough fibres, leading to a decrease in toughness by more than one order of magnitude. The reported necking mechanism may have broad implications also within more traditional melt-spinning research.
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| 3. |
- Andersson, Richard, et al.
(författare)
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Superparamagnetic [sic] nanofibers by electrospinning
- 2016
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 6:26, s. 21413-21422
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Tidskriftsartikel (refereegranskat)abstract
- The preparation of superparamagnetic thin fibers by electrospinning dispersions of nanosized magnetite (Fe3O4, SPIO/USPIO) in a PMMA/PEO polymer solution is reported. The saturation magnetization and coercivity were not affected by the concentration (0, 1, 10, 20 wt%) or fiber orientation, showing hysteresis loops with high magnetization (64 A m(2) kg(-1) @ 500 kA m(-1)) and record low coercivity (20 A m(-1)). AC susceptibility measurements vs. temperature at frequencies from 60 to 2 kHz confirmed superparamagnetism. The mechanical properties were only slightly dependent on the particle concentration because the nanoparticles were separately encapsulated by the polymer. A uniform fibre fracture cross section was found at all the investigated particle contents, which suggests a strong interaction at the polymer/particle interface. A theoretical value of the magnetic low field susceptibility was calculated from the Langevin function and compared with measured values. The results show a distinct but concentration-independent anisotropy, favoring magnetization along the fiber orientation with no sign of exchange interaction, explained by complete nanoparticle separation. Superparamagnetism cannot be inferred from particle size alone, so a relevant interpretation and criterion for superparamagnetism is presented, in accordance with Neel's original definition. From the measurements, it can be concluded that magnetic characterization can be used to elucidate the material morphology beyond the resolution of available microscopy techniques (TEM and SEM).
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| 4. |
- Antonio, Capezza, et al.
(författare)
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Preparation and Comparison of Reduced Graphene Oxide and Carbon Nanotubes as Fillers in Conductive Natural Rubber for Flexible Electronics
- 2019
-
Ingår i: Omega. - : American Chemical Society (ACS). - 0030-2228 .- 1541-3764. ; 4:2
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Tidskriftsartikel (refereegranskat)abstract
- Conductive natural rubber (NR) nanocomposites were prepared by solvent-casting suspensions of reduced graphene oxide(rGO) or carbon nanotubes (CNTs), followed by vulcanization of the rubber composites. Both rGO and CNT were compatible as fillers in the NR as well as having sufficient intrinsic electrical conductivity for functional applications. Physical (thermal) and chemical reduction of GO were investigated, and the results of the reductions were monitored by X-ray photoelectron spectroscopy for establishing a reduction protocol that was useful for the rGO nanocomposite preparation. Field-emission scanning electron microscopy showed that both nanofillers were adequately dispersed in the main NR phase. The CNT composite displays a marked mechanical hysteresis and higher elongation at break, in comparison to the rGO composites for an equal fraction of the carbon phase. Moreover, the composite conductivity was always ca. 3-4 orders of magnitude higher for the CNT composite than for the rGO composites, the former reaching a maximum conductivity of ca. 10.5 S/m, which was explained by the more favorable geometry of the CNT versus the rGO sheets. For low current density applications though, both composites achieved the necessary percolation and showed the electrical conductivity needed for being applied as flexible conductors for a light-emitting diode.
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| 5. |
- Dahlberg, D, et al.
(författare)
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Measurements of the ferromagnetic/antiferromagnetic interfacial exchange energy in CO/CoO and Fe/FeF2 layers
- 1998
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 83:11, s. 6893-6895
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Tidskriftsartikel (refereegranskat)abstract
- Two measurement techniques, both relying on reversible rotations of the magnetization, have been used to determine the magnitude of the interfacial exchange energy (IEE) between ferromagnetic and antiferromagnetic (F/AF) layers. One technique is to use the anisotropic magnetoresistance to determine rotations of the magnetization away from the unidirectional easy axis, where the rotation is accomplished by applying external magnetic fields less than the effective F/AF exchange field. The second technique uses measurements of the ac susceptibility as a function of the angle between the ac field and the unidirectional exchange field. Both of the reversible process techniques result in values of the IEE larger (by as much as a factor of 10 in Co/CoO bilayers) than the traditional irreversible technique of measuring a shift in the hysteresis loop. The ac susceptibility technique was also used to measure one Fe/FeF2 bilayer. For this sample, the IEE values obtained by reversible and irreversible methods are equivalent.
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| 6. |
- Dastanpour, E., et al.
(författare)
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Crystallization behavior, soft magnetism and nanoindentation of Fe–Si–B–P–Cu alloy on Ni substitution
- 2021
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 851
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Tidskriftsartikel (refereegranskat)abstract
- The present work investigates how the substitution of Ni for Fe in the amorphous precursor of the high flux density Fe–Si–B–P–Cu (Nanomet®) alloy avoids the creation of detrimental pre-existing nuclei in the amorphous precursor as a step forward for improved amorphization capability, retains homogenous nanocrystalline structure with excellent soft magnetic properties, and affects the mechanical properties in terms of reduced hardness and Young's modulus. This has been achieved by adding Ni of various concentrations (0–8 atomic %). The investigation includes structural characterization, calorimetry, optimization of annealing temperature, extensive magnetic characterization and nanoindentation to assess the mechanical properties. The excellent soft magnetic properties demonstrate a strategy to deploy the nanocrystalline ribbons where freedom of device design is a limiting factor for electrodynamic energy conversion applications.
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| 7. |
- Dastanpour, Esmat, et al.
(författare)
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Non-isothermal nanocrystallization of Fe83.3Si4B8P4Cu0.7 (NANOMET (R)) alloy : modeling and the heating rate effect on magnetic properties
- 2020
-
Ingår i: Journal of Physics D. - : Institute of Physics Publishing (IOPP). - 0022-3727 .- 1361-6463. ; 53:21
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of the nanocrystallization of a Fe83.3Si4B8P4Cu0.7 amorphous alloy by using differential scanning calorimetry has been investigated by non-isothermal annealing in a wide heating rate range from 10 degrees C min(-1) to 200 degrees C min(-1). The amorphous alloy was prepared by melt-spinning and showed a two-stage crystallization. In the first crystallization stage, alpha-Fe nanocrystals are formed. This phase is responsible for the good soft magnetic properties. The activation energy during the crystallization of the alpha-Fe nanocrystalline phase was determined from an isoconversional approach, and was found to be distinctively varying during the crystallization. An attempt was made to model the crystallization in an interval where the activation energy is relatively constant. The Malek criterion indicated that the Kolmogorov-Johnson-Mehl-Avrami model is not appropriate, whereas the Sestak-Berggren model meets the criterion. The acquired model shows good agreement with the experimental results. The magnetic properties of annealed ribbons at different heating rates show an initially steep decrease of the coercivity (H-c) from 82 A m(-1) at a heating rate of 10 degrees C min(-1) to 20 A m(-1) above 100 degrees C min(-1), whereas saturation magnetization (M-s) is practically invariant at ca 175 Am-2 kg(-1). This dependence is explained as due to diminishing grain size with higher heating rates, which is further supported by x-ray diffraction measurements.
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| 8. |
- Dastanpour, E., et al.
(författare)
-
On the glass forming ability (GFA), crystallization behavior and soft magnetic properties of nanomet-substituted alloys
- 2020
-
Ingår i: Journal of Non-Crystalline Solids. - : ELSEVIER. - 0022-3093 .- 1873-4812. ; 529
-
Tidskriftsartikel (refereegranskat)abstract
- This study was aimed to investigate the effect of substitution of Fe with Co, C, and Mo on the glass forming ability (GFA), crystallization behavior, and magnetic properties of Fe-B-Si-P-Cu (Nanomet) alloy. The thermodynamic parameters, P-HS and P-HSS, were used to guide towards increased GFA. The P-HSS enhanced from -2.04 kJ/mol for Nanomet to -4.83 kJ/mol for a Co4C1Mo1 (at.%) substituted alloy. As a result, the critical quench rate reduced significantly, manifested as a drop of the required rotational speed from 3000 rpm to 2000 rpm. The temperature interval between two crystallization peaks enlarged for the substituted alloy, allowing a broader annealing range for nanocrystallization. The saturation magnetization (M-S) and the coercivity (H-C) were nearly maintained. This work confirms the relevance of the parameters P-HS and P-HSS to improve the GFA of the Nanomet alloy, and it is suggested that the same strategy can be applied for other alloys.
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| 9. |
- Dastanpour, Esmat, et al.
(författare)
-
Quantification of the anomalous crystallization and soft magnetic properties of Fe-Si-B-P-Cu (Nanomet) by isothermal calorimetry
- 2020
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 830
-
Tidskriftsartikel (refereegranskat)abstract
- The present study aimed to quantify the anomalous crystallization and soft magnetic properties of Fe-Si-B-P-Cu (Nanomet) alloy by isothermal calorimetry. The isothermal crystallization had slow kinetics at temperatures below the peak temperature of the exothermic event. The inhomogeneous distribution of pre-existing nuclei in the amorphous structure led to the anomalous crystallization, and hence, to a nonlinear Avrami plot with lowered localized Avrami exponents, attributed to temperature dependent crystallization kinetics. To the best of our knowledge, the presence of pre-existing magnetic nuclei was experimentally confirmed for the first time using ultra-high sensitive magneto-thermo-gravimetry (MTG). This is otherwise challenging, if not impossible, with conventional structural diffraction techniques. The incremental saturation magnetization (Ms) revealed how the volume fraction of the nanocrystallites intrinsically depends on both the annealing temperature and dwell time, and the significant change in the coercivity (He) confirmed the vital role the homogenous nucleation growth process has in order to achieve excellent soft magnetic properties.
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| 10. |
- Dastanpour Hosseinabadi, Esmat, et al.
(författare)
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An assessment of the Al50Cr21-xMn17+xCo12 (x=0, 4, 8) high-entropy alloys for magnetocaloric refrigeration application
- 2024
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 984
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the magnetocaloric potential of the Al50Cr21-xMn17+xCo12 (x=0, 4, 8 at%) high-entropy alloy (HEA) series using integrated experimental and theoretical approaches. Structural analysis by X-ray diffraction and scanning electron microscopy indicate a dual phase containing B2 and body-centered cubic (BCC) structures. Magnetic characterization shows an approximately linear decrease in saturation magnetization and Curie temperature with increasing Cr content. Curie temperatures calculated by Monte Carlo simulations suggest that the measured magnetic properties originate from the B2 phase rather than the BCC phase. The enhanced magnetocaloric effect with decreasing Cr content highlights the attractiveness of HEAs in magnetocaloric applications.
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| 11. |
- Dastanpour Hosseinabadi, Esmat, et al.
(författare)
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Investigation of the metastable spinodally decomposed magnetic CrFe-rich phase in Al doped CrFeCoNi alloy
- 2023
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 939
-
Tidskriftsartikel (refereegranskat)abstract
- We have conducted an in-depth study of the magnetic phase due to a spinodal decomposition of the BCC phase of a CrFe-rich composition. This magnetic phase is present after casting (arc melting) or water quenching after annealing at 1250 degrees C for 24 h but is entirely absent after annealing in the interval 900-1100 degrees C for 24 h. Its formation is favored in the temperature interval ca 450-550 degrees C and loses magnetization above 640 degrees C. This ferromagnetic-paramagnetic transition is due to a structural transformation from ferromagnetic BCC into paramagnetic sigma and FCC phases. The conclusion from measurements at different heating rates is that both the transformation leading to the increase of the magnetization due to the spinodal decomposition of the parent phase and the vanishing magnetization at 640 degrees C are diffusion controlled. (c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).
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| 12. |
- Dastanpour Hosseinabadi, Esmat, et al.
(författare)
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Multi-alloying of nanomet : conception and implementation of homogeneous nanocrystallization in high-flux density soft magnetic alloys
- 2021
-
Ingår i: Journal of Materials Science. - : Springer. - 0022-2461 .- 1573-4803. ; 56:16, s. 10124-10134
-
Tidskriftsartikel (refereegranskat)abstract
- This study demonstrates how multi-alloying the Fe-Si–B–P–Cu (Nanomet®) can avoid the strict requirements on the annealing scheme in terms of high heating rate and narrow annealing temperature range in order to grow a homogeneous ultrafine nanocrystalline structure. The rather restricted amorphization capability sets a low limit of the maximum thickness of the amorphous precursor. These shortcomings have their origin in the existence of detrimental pre-existing nuclei in the amorphous precursors, which in turn potentially lead to a heterogeneous crystallization. Here, we have multialloyed Nanomet with CoCNi- and CoCMo- to avoid the creation of these pre-existing nuclei. This leads to improved amorphization capability and changes a potentially heterogeneous crystallization to a homogeneous nanocrystallization over a much broader temperature range than for unalloyed Nanomet. Thus, the requirements for the annealing are much relaxed. This work encompasses quenching the amorphous precursors using melt-spinning, investigating the crystallization temperatures by calorimetry, showing the depletion of pre-existing nuclei by magneto-thermo-gravimetry, conceptualizing the crystallization dynamics using isothermal calorimetry, and finally revealing the excellent soft magnetic properties over a broad annealing temperature interval (390–490 °C for the substituted alloys compared to 410–470 °C for unalloyed Nanomet). The multi-elemental substitution of Fe with CoCMo and CoCNi in Nanomet alloy nearly maintains the saturation magnetization and the coercivity. We believe the substituted alloys provide a better alternative to Nanomet with improved amorphization capability and homogeneous nanocrystallization without any special heat treatment scheme. Graphical abstract: [Figure not available: see fulltext.]
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| 13. |
- Dastanpour Hosseinabadi, Esmat, et al.
(författare)
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On the structural and magnetic properties of Al-rich high entropy alloys : a joint experimental-theoretical study
- 2023
-
Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 56:1
-
Tidskriftsartikel (refereegranskat)abstract
- The present work investigates how the vanadium (V) content in a series of Al50V (x) (Cr0.33Mn0.33Co0.33)((50-x)) (x = 12.5, 6.5, 3.5, and 0.5 at.%) high-entropy alloys affects the local magnetic moment and magnetic transition temperature as a step towards developing high-entropy functional materials for magnetic refrigeration. This has been achieved by carrying out experimental investigations on induction melted alloys and comparison to ab initio and thermodynamic calculations. Structural characterization by x-ray diffraction and scanning electron microscopy indicates a dual-phase microstructure containing a disordered body-centered cubic (BCC) phase and a B2 phase with long-range order, which significantly differ in the Co and V contents. Ab initio calculations demonstrate a weaker magnetization and lower magnetic transition temperature (T
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| 14. |
- Dong, Zhihua, et al.
(författare)
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MnxCr0.3Fe0.5Co0.2Ni0.5Al0.3 high entropy alloys for magnetocaloric refrigeration near room temperature
- 2021
-
Ingår i: Journal of Materials Science & Technology. - : Chinese Society of Metals. - 1005-0302. ; 79, s. 15-20
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Tidskriftsartikel (refereegranskat)abstract
- High entropy alloys (HEAs) based on transition metals display rich magnetic characteristics, however attempts on their application in energy efficient technologies remain scarce. Here, we explore the magnetocaloric application for a series of MnxCr0.3Fe0.5Co0.2Ni0.5Al0.3 (0.8 < x < 1.1) HEAs by integrated theoretical and experimental methods. Both theory and experiment indicate the designed HEAs have the Curie temperature close to room temperature and is tunable with Mn concentration. A non-monotonic evolution is observed for both the entropy change and the relative cooling power with changing Mn concentration. The underlying atomic mechanism is found to primarily emerge from the complex impact of Mn on magnetism. Advanced magnetocaloric properties can be achieved by tuning Mn concentration in combination with controlling structural phase stability for the designed HEAs.
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| 15. |
- Fang, Mei, 1984-, et al.
(författare)
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Co-precipitation of iron oxide nanoparticles by rapid mixing
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Synthesis of Magnetite appears to be a topic of continued interest because of its versatility and the variety applications. Among the chemical techniques to synthesize Fe3O4, co-precipitation approach although very common, seems to be extremely sensitive to the consequences of nucleation, growth and most of all the rate of the reaction involved. This work is an attempt to demonstrate the complexities of obtaining monodispersed nanosized Fe3O4 particles. We consider the role of rapid mixing and its consequences on co-precipitation at ice-point, room temperature and boiling water temperatures on the magnetic properties of Fe3O4. We obtained crystallites varying in the range from 6.6 nm (grown in ice-water) to 7.9 nm (grown in boiling water) as determined from the broadening of XRD diffraction peaks using the Scherrer approach. With the increase of the particle size, the saturate magnetization of iron oxides increases from 52 emu/g to 63 emu/g, and the coercivity increases from 0.5 Oe to 7.9 Oe. Layers of nanosized magnetic particles on glass substrates show unusual wavelength dependence of Faraday rotation loops which show a reversal phenomenon in the sign of the magnetization around 550.
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| 16. |
- Fang, Mei, et al.
(författare)
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Particle size and magnetic properties dependence on growth temperature for rapid mixed co-precipitated magnetite nanoparticles
- 2012
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 23:14, s. 145601-
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Tidskriftsartikel (refereegranskat)abstract
- Magnetite nanoparticles have been prepared by co-precipitation using a custom-designed jet mixer to achieve rapid mixing (RM) of reactants in a timescale of milliseconds. The quick and stable nucleation obtained allows control of the particle size and size distribution via a more defined growth process. Nanoparticles of different sizes were prepared by controlling the processing temperature in the first few seconds post-mixing. The average size of the nanoparticles investigated using a Tecnai transmission electron microscope is found to increase with the temperature from 3.8 nm at 1 +/- 1 degrees C to 10.9 nm for particles grown at 95 +/- 1 degrees C. The temperature dependence of the size distribution follows the same trend and is explained in terms of Ostwald ripening of the magnetite nanoparticles during the co-precipitation of Fe2+ and Fe3+. The magnetic properties were studied by monitoring the blocking temperature via both DC and AC techniques. Strikingly, the obtained RM particles maintain the high magnetization (as high as similar to 88 A m(2) kg(-1) at 500 kA m(-1)) while the coercivity is as low as similar to 12 A m(-1) with the expected temperature dependence. Besides, by adding a drop of tetramethylammonium hydroxide, aqueous ferrofluids with long term stability are obtained, suggesting their suitability for applications in ferrofluid technology and biomedicine.
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| 17. |
- Fang, Mei, et al.
(författare)
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Rapid mixing : A route to synthesize magnetite nanoparticles with high moment
- 2011
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 99:22, s. 222501-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the impact of rapid mixing of the precursors in a time scale of milliseconds on the reaction rate and magnetic properties of co-precipitated magnetite with a custom-made mixer. The mixed volume is directed into a desk-top AC susceptometer to monitor the magnetic response from the growing particles in real-time. These measurements indicate that the reaction is mostly completed within a minute. The obtained superparamagnetic nanoparticles exhibit a narrow size distribution and large magnetization (87 Am(2) kg(-1)). Transmission electron micrographs suggest that rapid mixing is the key for better crystallinity and a more uniform morphology leading to the observed magnetization values.
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| 18. |
- Galland, Sylvain, 1987-, et al.
(författare)
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Cellulose nanofibers decorated with magnetic nanoparticles : synthesis, structure and use in magnetized high toughness membranes for a prototype loudspeaker
- 2013
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Ingår i: Journal of Materials Chemistry C. - 2050-7526. ; 1:47, s. 7963-7972
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic nanoparticles are the functional component for magnetic membranes, but they are difficult to disperse and process into tough membranes. Here, cellulose nanofibers are decorated with magnetic ferrite nanoparticles formed in situ which ensures a uniform particle distribution, thereby avoiding the traditional mixing stage with the potential risk of particle agglomeration. The attachment of the particles to the nanofibrils is achieved via aqueous in situ hydrolysis of metal precursors onto the fibrils at temperatures below 100 °C. Metal adsorption and precursor quantification were carried out using Induction Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). FE-SEM was used for high resolution characterization of the decorated nanofibers and hybrid membranes, and TEM was used for nanoparticle size distribution studies. The decorated nanofibers form a hydrocolloid. Large (200 mm diameter) hybrid cellulose/ferrite membranes were prepared by simple filtration and drying of the colloidal suspension. The low-density, flexible and permanently magnetized membranes contain as much as 60 wt% uniformly dispersed nanoparticles (thermogravimetric analysis data). Hysteresis magnetization was measured by a Vibrating Sample Magnetometer; the inorganic phase was characterized by XRD. Membrane mechanical properties were measured in uniaxial tension. An ultrathin prototype loudspeaker was made and its acoustic performance in terms of output sound pressure was characterized. A full spectrum of audible frequencies was resolved.
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| 19. |
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| 20. |
- Galland, Sylvain, 1987-, et al.
(författare)
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Strong and Moldable Cellulose Magnets with High Ferrite Nanoparticle Content
- 2014
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 6:22, s. 20524-20534
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Tidskriftsartikel (refereegranskat)abstract
- A major limitation in the development of highly functional hybrid nanocomposites is brittleness and low tensile strength at high inorganic nanoparticle content. Herein, cellulose nanofibers were extracted from wood and individually decorated with cobalt-ferrite nanoparticles and then for the first time molded at low temperature (<120 degrees C) into magnetic nanocomposites with up to 93 wt % inorganic content. The material structure was characterized by TEM and FE-SEM and mechanically tested as compression molded samples. The obtained porous magnetic sheets were further impregnated with a thermosetting epoxy resin, which improved the load-bearing functions of ferrite and cellulose material. A nanocomposite with 70 wt % ferrite, 20 wt % cellulose nanofibers, and 10 wt % epoxy showed a modulus of 12.6 GPa, a tensile strength of 97 MPa, and a strain at failure of ca. 4%. Magnetic characterization was performed in a vibrating sample magnetometer, which showed that the coercivity was unaffected and that the saturation magnetization was in proportion with the ferrite content. The used ferrite, CoFe2O4 is a magnetically hard material, demonstrated by that the composite material behaved as a traditional permanent magnet. The presented processing route is easily adaptable to prepare millimeter-thick and moldable magnetic objects. This suggests that the processing method has the potential to be scaled-up for industrial use for the preparation of a new subcategory of magnetic, low-cost, and moldable objects based on cellulose nanofibers.
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| 21. |
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| 22. |
- Guex, Leonard Gaston, et al.
(författare)
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Experimental review : chemical reduction of graphene oxide (GO) to reduced graphene oxide (rGO) by aqueous chemistry
- 2017
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 9:27, s. 9562-9571
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Forskningsöversikt (refereegranskat)abstract
- The electrical conductivity of reduced graphene oxide (rGO) obtained from graphene oxide (GO) using sodium borohydride (NaBH4) as a reducing agent has been investigated as a function of time (2 min to 24 h) and temperature (20 degrees C to 80 degrees C). Using a 300 mM aqueous NaBH4 solution at 80 degrees C, reduction of GO occurred to a large extent during the first 10 min, which yielded a conductivity increase of 5 orders of magnitude to 10 S m(-1). During the residual 1400 min of reaction, the reduction rate decreased significantly, eventually resulting in a rGO conductivity of 1500 S m(-1). High resolution XPS measurements showed that C/O increased from 2.2 for the GO to 6.9 for the rGO at the longest reaction times, due to the elimination of oxygen. The steep increase in conductivity recorded during the first 8-12 min of reaction was mainly due to the reduction of C-O (e.g., hydroxyl and epoxy) groups, suggesting the preferential attack of the reducing agent on C-O rather than C=O groups. In addition, the specular variation of the percentage content of C-O bond functionalities with the sum of Csp(2) and Csp(3) indicated that the reduction of epoxy or hydroxyl groups had a greater impact on the restoration of the conductive nature of the graphite structure in rGO. These findings were reflected in the dramatic change in the structural stability of the rGO nanofoams produced by freeze-drying. The reduction protocol in this study allowed to achieve the highest conductivity values reported so far for the aqueous reduction of graphene oxide mediated by sodium borohydride. The 4-probe sheet resistivity approach used to measure the electrical conductivity is also, for the first time, presented in detail for filtrate sheet assemblies' of stacked GO/rGO sheets.
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| 23. |
- Hoogendoorn, Billy W., et al.
(författare)
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Cellulose nanofibers (CNFs) in the recycling of nickel and cadmium battery metals using electrodeposition
- 2023
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Ingår i: Nanoscale Advances. - : Royal Society of Chemistry (RSC). - 2516-0230. ; 5:19, s. 5263-5275
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose nanofibers (CNFs) were employed in the aqueous electrodeposition of nickel and cadmium for battery metal recycling. The electrowinning of mixed Ni-Cd metal ion recycling solutions demonstrated that cadmium with a purity of over 99% could be selectively extracted while leaving the nickel in the solution. Two types of CNFs were evaluated: negatively charged CNFs (a-CNF) obtained through acid hydrolysis (−75 μeq. g−1) and positively charged CNFs (q-CNF) functionalized with quaternary ammonium groups (+85 μeq. g−1). The inclusion of CNFs in the Ni-Cd electrolytes induced growth of cm-sized dendrites in conditions where dendrites were otherwise not observed, or increased the degree of dendritic growth when it was already present to a lesser extent. The augmented dendritic growth correlated with an increase in deposition yields of up to 30%. Additionally, it facilitated the formation of easily detachable dendritic structures, enabling more efficient processing on a large scale and enhancing the recovery of the toxic cadmium metal. Regardless of the charged nature of the CNFs, both negatively and positively charged CNFs led to a significant formation of protruding cadmium dendrites. When deposited separately, dendritic growth and increased deposition yields remained consistent for the cadmium metal. However, dendrites were not observed during the deposition of nickel; instead, uniformly deposited layers were formed, albeit at lower yields (20%), when positively charged CNFs were present. This paper explores the potential of utilizing cellulose and its derivatives as the world's largest biomass resource to enhance battery metal recycling processes.
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| 24. |
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| 25. |
- Hoogendoorn, Billy W., et al.
(författare)
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Ultra-low Concentration of Cellulose Nanofibers (CNFs) for Enhanced Nucleation and Yield of ZnO Nanoparticles
- 2022
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 38:41, s. 12480-12490
-
Tidskriftsartikel (refereegranskat)abstract
- Cellulose nanofibers (CNFs) were used in aqueous synthesis protocols for zinc oxide (ZnO) to affect the formation of the ZnO particles. Different concentrations of CNFs were evaluated in two different synthesis protocols producing distinctly different ZnO morphologies (flowers and sea urchins) as either dominantly oxygen-or zinc-terminated particles. The CNF effects on the ZnO formation were investigated by implementing a heat-treatment method at 400 degrees C that fully removed the cellulose material without affecting the ZnO particles made in the presence of CNFs. The inorganic phase formations were monitored by extracting samples during the enforced precipitations to observe changes in the ZnO morphologies. A decrease in the size of the ZnO particles could be observed for all synthesis protocols, already occurring at small additions of CNFs. At as low as 0.1 g/L CNFs, the particle size decreased by 50% for the flower-shaped particles and 45% for the sea-urchin-shaped particles. The formation of smaller particles was accompanied by increased yield by 13 and 15% due to the CNFs' ability to enhance the nucleation, resulting in greater mass of ZnO divided among a larger number of particles. The enhanced nucleation could also be verified as useful for preventing secondary morphologies from forming, which grew on the firstly precipitated particles. The suppression of secondary growths' was due to the more rapid inorganic phase formation during the early phases of the reactions and the faster consumption of dissolved salts, leaving smaller amounts of metal salts present at later stages of the reactions. The findings show that using cellulose to guide inorganic nanoparticle growth can be predicted as an emerging field in the preparation of functional inorganic micro/nanoparticles. The observations are highly relevant in any industrial setting for the large-scale and resource-efficient production of ZnO.
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| 26. |
- Hou, Ziyong, et al.
(författare)
-
Effect of carbon content on the Curie temperature of WC-NiFe cemented carbides
- 2019
-
Ingår i: International journal of refractory metals & hard materials. - : Elsevier. - 0263-4368. ; 78, s. 27-31
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the effect of the carbon content on the Curie temperature of a cemented carbide composite material with a Ni-Fe alloy as the binder phase and WC as the hard phase. In the carbon concentration range from 5.72 to 5.83 wt% carbon, which covers the interval where WC coexists with fcc Ni-Fe without other phases (the ‘carbon window’), the Curie temperature rises from 200 to 527 °C. This result indicates the possibility to use the Curie temperature to determine the carbon balance in the system. With thermodynamic calculations and kinetic simulations we can quantitatively establish the correlation between the carbon and tungsten content of the binder phase and the Curie temperature. This strong compositional effect on the Curie temperature is quantitatively very different from the conventional Co-based cemented carbides, with Curie temperatures of about 950–1050 °C.
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| 27. |
- Hou, Ziyong, 1986-, et al.
(författare)
-
Evaluating magnetic properties of composites from model alloys – Application to alternative binder cemented carbides
- 2019
-
Ingår i: Scripta Materialia. - : Acta Materialia Inc. - 1359-6462 .- 1872-8456. ; 168, s. 96-99
-
Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of 85Ni-15Fe model alloys containing Co, W and C have been studied with the intent to isolate the influence of alloy chemistry on quality control measurements of alternative binder cemented carbides. The results show a strong influence of dissolved W on the Curie temperature and the saturation magnetization. The amount of dissolved C, and the presence of WC precipitates, on the other hand, is shown to have negligible effect. Furthermore, the magnetic coercivity is indicated to be entirely dominated by the microstructural features and quite insensitive to composition.
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| 28. |
- Huang, Shuo, et al.
(författare)
-
Combinatorial design of partial ordered Al-Cr-Mn-Co medium-entropy alloys for room temperature magnetic refrigeration applications
- 2023
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 123:4
-
Tidskriftsartikel (refereegranskat)abstract
- Multi-component alloys have received increasing interest for functional applications in recent years. Here, we explore the magnetocaloric response for Al-Cr-Mn-Co medium-entropy alloys by integrated theoretical and experimental methods. Under the guidance of thermodynamic and ab initio calculations, a dual-phase system with large magnetic moment, i.e., Al50Cr19Mn19Co12, is synthesized, and the structural and magnetocaloric properties are confirmed via characterization. The obtained results indicate that the selected alloy exhibits a co-continuous mixture of a disordered body-centered cubic and an ordered B2 phase. The ab initio and Monte Carlo calculations indicate that the presence of the ordered B2 phase is responsible for the substantial magnetocaloric effect. The magnetization measurements demonstrated that this alloy undergoes a second-order magnetic transition with the Curie temperature of similar to 300 K. The magnetocaloric properties are examined using magnetic entropy change, refrigeration capacity, and adiabatic temperature change. The property-directed strategy explored here is intended to contribute to the study of potential multi-component alloys in magnetocaloric applications.
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| 29. |
- Huang, Shuo, et al.
(författare)
-
Magnetocaloric properties of melt-spun MnFe-rich high-entropy alloy
- 2021
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 119:14
-
Tidskriftsartikel (refereegranskat)abstract
- High-entropy functional materials are of great interest in materials science and engineering community. In this work, ab initio electronic structure calculations of the phase stability and magnetic transition temperature of AlxCr0.25MnFeCo0.25-yNiy (x = 0-0.5, y = 0-0.25) alloys were performed to screen for compositions showing promising magnetocaloric properties in the vicinity of room temperature. The selected Al0.44Cr0.25MnFeCo0.05Ni0.2 alloy was synthesized via a rapid solidification technique and systematically characterized with respect to its structural and magnetocaloric properties. The results indicate that this alloy possesses a homogeneous microstructure based on an underlying body-centered cubic lattice and has a Curie temperature of & SIM;340 K. The temperature dependence of the adiabatic temperature change was evaluated using both direct and indirect methods. The ab initio-assisted design of 3d-metal-based high-entropy alloys, explored here, is intended to contribute to the development of magnetic refrigerators for room-temperature applications.
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| 30. |
- Huang, Shou, et al.
(författare)
-
Thermo-elastic Properties of BCC Mn-rich High-entropy Alloy
- 2020
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 117:16
-
Tidskriftsartikel (refereegranskat)abstract
- We report a chemically disordered solid solution, Al0.6Cr0.2MnFe0.5Co0.3Ni0.5, based on a body-centered cubic underlying lattice with the measured Curie temperature of ∼380 K. First-principles alloy theory is employed to investigate the temperature-dependent free energy, elastic constants, and coefficient of thermal expansion at the ferromagnetic and paramagnetic states. Theory and experiment are found to strengthen each other, and the results indicate that the magnetic state has a strong impact on the thermo-elastic properties of the considered alloy. The present advance in the thermo-magneto-elasticity enhances the understanding required for controlling the magnetic and mechanical response of multi-component systems.
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| 31. |
- Huang, Shuo, et al.
(författare)
-
Vibrational entropy-enhanced magnetocaloric effect in Mn-rich high-entropy alloys
- 2021
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 119:8
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the AlxCr0.2MnFe0.5Co0.3Ni0.5 (0.3 <= x <= 0.7) high-entropy alloys by combining experimental and theoretical techniques. X-ray diffraction and magnetization measurements indicate that Al alters the crystal structure and the entropy change upon magnetization-demagnetization while keeping the Curie temperature almost unchanged. First-principles calculations of the vibrational, magnetic, electronic, and configurational entropies show that the leading entropy change is due to the magnetic and vibrational degrees of freedom. The presence of the body-centered-cubic phase, showing a sizable elastic softening upon magnetic transition, brings about the substantial magnetocaloric effect in this family of alloys.
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| 32. |
- Johnson, Kyle, et al.
(författare)
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Oxidation of accident tolerant fuel candidates
- 2017
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Ingår i: Journal of Nuclear Science and Technology. - : Taylor & Francis. - 0022-3131 .- 1881-1248. ; 54:3, s. 280-286
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the oxidation of various accident tolerant fuel candidates produced under different conditions have been evaluated and compared relative to the reference standard–UO2. The candidates considered in this study were UN, U3Si2, U3Si5, and a composite material composed of UN–U3Si2. With the spark plasma sintering (SPS) method, it was possible to fabricate samples of UN with varying porosity, as well as a high-density composite of UN–U3Si2 (10%). Using thermogravimetry in air, the oxidation behaviors of each material and the various microstructures of UN were assessed. These results reveal that it is possible to fabricate UN to very high densities using the SPS method, such that its resistance to oxidation can be improved compared to U3Si5 and UO2, and compete favorably with the principal ATF candidates, U3Si2, which shows a particularly violent reaction under the conditions of this study, and the UN–U3Si2 (10%) composite.
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| 33. |
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| 34. |
- Kapilashrami, Mukes, et al.
(författare)
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Effect of synthesis techniques on the magnetic properties of Mn-doped ZnO
- 2008
-
Ingår i: Magnetic Materials. - : AIP. - 9780735405226 ; , s. 255-257
-
Konferensbidrag (refereegranskat)abstract
- Mn-doped ZnO thin films have been prepared using three different routes, namely, magnetron sputtering technique, Pulsed Laser Deposition technique using targets from powders synthesized by solid state, and chemical method. Films deposited using sputtering technique in absence of nitrogen pressure gives higher magnetic moment per Mn atom, than is the case with films prepared by PLD indicating that ferromagnetism in the DMS systems is highly sensitive to processing conditions.
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| 35. |
- Kapilashrami, Mukes, et al.
(författare)
-
On the defect induced ferromagnetic ordering above room-temperature in undoped and Mn doped ZnO thin films
- 2009
-
Ingår i: NOVEL MATERIALS AND DEVICES FOR SPINTRONICS. - Warrendale, PA : MATERIALS RESEARCH SOCIETY. ; , s. 3-8
-
Konferensbidrag (refereegranskat)abstract
- Evidence for long range ferromagnetic order above room-temperature, RTFM, in pristine ZnO, In2O3, TiO2 nanoparticles and thin films, containing no nominal magnetic elements have been reported recently. This could question the origin of RTFM in doped dilute alloys if for example the ZnO matrix itself develops a defect induced magnetic order with a significant moment per unit cell. In this presentation we report a systematic study of the film thickness dependence of RTFM in pure ZnO deposited by DC Magnetron Sputtering. We observe a maximum in the saturation magnetization, Ms, value of 0.62 emu/g (0,018 ÎŒB/unit cell), for a -480 nm film deposited in an oxygen ambience of appropriate pressure. Above a thickness of around 1 ÎŒm the films are diamagnetic as expected. We thus see a sequential transition from ferromagnetism to para- and eventual diamagnetism as a function of film thickness in ZnO. We also find that in such a ZnO matrix with a maximum intrinsic defect induced moment, on doping with Mn the maximum enhanced Ms value of 0.78 emu/g is obtained for 1 at. % Mn doping. With this approach of appropriate doping in a defect tailored matrix, we routinely obtain RTFM in both undoped and Mn- doped ZnO thin films.
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| 36. |
- Kapilashrami, Mukes, et al.
(författare)
-
Transition from ferromagnetism to diamagnetism in undoped ZnO thin films
- 2009
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:3
-
Tidskriftsartikel (refereegranskat)abstract
- We report a systematic study of the film thickness dependence (0.1-1 mu m) of room-temperature ferromagnetism in pure magnetron-sputtered ZnO thin films wherein a sequential transition from ferromagnetism to paramagnetism and diamagnetism as a function of film thickness is observed. The highest saturation magnetization (M-S) value observed is 0.62 emu/g (0.018 mu(B)/unit cell) for a similar to 480 nm film. On doping the ZnO film with 1 at. % Mn enhances the M-S value by 26%. The ferromagnetic order in ZnO matrix is believed to be defect induced. In addition, on doping with Mn hybridization between the 2p states of O and the 3d states of Mn occurs.
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| 37. |
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| 38. |
- Karlsson, Mattias E., et al.
(författare)
-
Lamellae-controlled electrical properties of polyethylene - morphology, oxidation and effects of antioxidant on the DC conductivity
- 2020
-
Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 10:8, s. 4698-4709
-
Tidskriftsartikel (refereegranskat)abstract
- Destruction of the spherulite structure in low-density polyethylene (LDPE) is shown to result in a more insulating material at low temperatures, while the reverse effect is observed at high temperatures. On average, the change in morphology reduced the conductivity by a factor of 4, but this morphology-related decrease in conductivity was relatively small compared with the conductivity drop of more than 2 decades that was observed after slight oxidation of the LDPE (at 25 degrees C and 30 kV mm(-1)). The conductivity of LDPE was measured at different temperatures (25-60 degrees C) and at different electrical field strengths (3.3-30 kV mm(-1)) for multiple samples with a total crystalline content of 51 wt%. The transformation from a 5 mu m coherent structure of spherulites in the LDPE to an evenly dispersed random lamellar phase (with retained crystallinity) was achieved by extrusion melt processing. The addition of 50 ppm commercial phenolic antioxidant to the LDPE matrix (e.g. for the long-term use of polyethylene in high voltage direct current (HVDC) cables) gave a conductivity ca. 3 times higher than that of the same material without antioxidants at 60 degrees C (the operating temperature for the cables). For larger amounts of antioxidant up to 1000 ppm, the DC conductivity remained stable at ca. 1 x 10(-14) S m(-1). Finite element modeling (FEM) simulations were carried out to model the phenomena observed, and the results suggested that the higher conductivity of the spherulite-containing LDPE stems from the displacement and increased presence of polymeric irregularities (formed during crystallization) in the border regions of the spherulite structures.
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| 39. |
- Karlsson, Mattias E., et al.
(författare)
-
Synthesis of Zinc Oxide Nanorods via the Formation of Sea Urchin Structures and Their Photoluminescence after Heat Treatment
- 2018
-
Ingår i: Langmuir. - : AMER CHEMICAL SOC. - 0743-7463 .- 1520-5827. ; 34:17, s. 5079-5087
-
Tidskriftsartikel (refereegranskat)abstract
- A protocol for the aqueous synthesis of ca. 1-mu m-long zinc oxide (ZnO) nanorods and their growth at intermediate reaction progression is presented, together with photoluminescence (PL) characteristics after heat treatment at temperatures of up to 1000 degrees C. The existence of solitary rods after the complete reaction (60 min) was traced back to the development of sea urchin structures during the first 5 s of the precipitation. The rods primarily formed in later stages during the reaction due to fracture, which was supported by the frequently observed broken rod ends with sharp edges in the final material, in addition to tapered uniform rod ends consistent with their natural growth direction. The more dominant rod growth in the c direction (extending the length of the rods), together with the appearance of faceted surfaces on the sides of the rods, occurred at longer reaction times (>5 min) and generated zinc-terminated particles that were more resistant to alkaline dissolution. A heat treatment for 1 h at 600 or 800 degrees C resulted in a smoothing of the rod surfaces, and PL measurements displayed a decreased defect emission at ca. 600 nm, which was related to the disappearance of lattice imperfections formed during the synthesis. A heat treatment at 1000 degrees C resulted in significant crystal growth reflected as an increase in luminescence at shorter wavelengths (ca. 510 nm). Electron microscopy revealed that the faceted rod structure was lost for ZnO rods exposed to temperatures above 600 degrees C, whereas even higher temperatures resulted in particle sintering and/or mass redistribution along the initially long and slender ZnO rods. The synthesized ZnO rods were a more stable Wurtzite crystal structure than previously reported ball-shaped ZnO consisting of merging sheets, which was supported by the shifts in PL spectra occurring at ca. 200 degrees C higher annealing temperature, in combination with a smaller thermogravimetric mass loss occurring upon heating the rods to 800 degrees C.
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| 40. |
- Karlsson, Mattias E., et al.
(författare)
-
The effect of ZnO particle lattice termination on the DC conductivity of LDPE nanocomposites
- 2020
-
Ingår i: Materials Advances. - : Royal Society of Chemistry (RSC). - 2633-5409. ; 1:6, s. 1653-1664
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of particle surface termination by zinc or oxygen were evaluated for composites containing micro-sized ZnO particles with rod shapes (17% oxygen terminations) or ball shapes (67% oxygen terminations), and it was found that the rods gave a conductivity (1.2 x 10(-16) S m(-1)) half that given by the ball-shaped particles (2.4 x 10(-16) S m(-1)). Both composites containing the micro-sized particles showed a conductivity almost two orders of magnitude lower than that of the LDPE reference material (1.2 x 10(-14) S m(-1)). When a 5 nm thick silica coating was applied to the particles, the silica encapsulation eliminated the difference between the particles and resulted in both cases in an increase in conductivity by an order of magnitude to ca. 2 x 10(-15) S m(-1). The conductivity was still lower than that of the pristine polyethylene polymer. It was concluded that neither the particle morphology nor the inter-particle distance (1 mu m for rods and 8 mu m for balls) had any effect on the conductivity of the composites for identically terminated particles, while demonstrating that the conductivity of these materials relies uniquely on the particle surface terminations. In contrast, a markedly reduced conductivity was observed for composites containing the same particles but terminated with aliphatic hydrocarbon tails, the conductivity for both rod-shaped and ball-shaped particles (1 x 10(-16) S m(-1)) being reduced to even lower values than for the pristine particles without surface modification. The same trend was observed with the 25 nm ZnO nanoparticles, showing a record low conductivity of 1 x 10(-17) S m(-1) for 3 wt% nanoparticles with aliphatic hydrocarbon tails. In practical applications, this would permit higher operation voltages than currently employed HVDC cable systems by controlling the resistivity of the composite insulation for various electric fields and temperatures and making it possible to tailor the dielectric design of cable components.
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| 41. |
- Lee, Sangmin, et al.
(författare)
-
Magneto-Thermo-Gravimetric technique to investigate the structural and magnetic properties of Fe-B-Nb-Y Bulk Metallic Glass
- 2009
-
Ingår i: 13TH INTERNATIONAL CONFERENCE ON RAPIDLY QUENCHED AND METASTABLE MATERIALS. - : IOP Publishing. ; , s. 012074-
-
Konferensbidrag (refereegranskat)abstract
- Magneto-thermo-gravimetric (MTG) technique is highly informative about the changes in the magnetic state, as well as structural changes in a system, which cannot be often noticed in calorimetric measurements. We demonstrate the versatility of this technique in determining the magnetic transition temperature, and the subsequent crystallization process in a (Fe(0.72)B(0.24)Nb(0.04))(95.5)Y(4.5) Bulk Metallic Glass (BMG). MTG and DSC analyses were carried out at the heating rate of 0.67 K/s from RT similar to 1170 K. As a result of the repeated MTG measurements, a magnetic 2(nd) amorphous phase was observed in the BMG sample, which could be the first measurement for the Magnetic Short Range Ordering (MSRO). Consequently, the MTG measurement is proved as the most convenient method for determining the various structural and magnetic transitions in a glassy material.
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| 42. |
- Linder, David, et al.
(författare)
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A comparative study of microstructure and magnetic properties of a Ni–Fe cemented carbide : Influence of carbon content
- 2019
-
Ingår i: International journal of refractory metals & hard materials. - : Elsevier Ltd. - 0263-4368. ; 80, s. 181-187
-
Tidskriftsartikel (refereegranskat)abstract
- Due to the renewed interest in alternative binders for cemented carbides it is important to understand how the binder composition influences not only mechanical properties but also the microstructure and related measurements for quality control. Microstructure and chemical composition of WC-Co is often evaluated by magnetic measurements. However, when the binder composition deviates significantly from conventional Co-based binders it should not be assumed that the standard measurements can be used to directly evaluate the same parameters. In this paper we investigate the influence of relative C-content on the microstructure and magnetic properties of an alternative binder cemented carbide. It is shown that the saturation magnetization is related to the relative C-content and the magnetic coercivity is related to the microstructure, more specifically to the binder phase distribution, but could not be directly linked to the carbide grain size in the same manner as for standard WC-Co. Furthermore, a direct correlation between Curie temperature and saturation magnetization is observed for this system which means that the Curie temperature potentially could be used for calibration of empirical relations or as a method to accurately determine the binder volume fraction.
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| 43. |
- Ma, Taoran, et al.
(författare)
-
Self-organizing nanostructured lamellar (Ti,Zr)C - A superhard mixed carbide
- 2015
-
Ingår i: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 51, s. 25-28
-
Tidskriftsartikel (refereegranskat)abstract
- A nanoindentation and first-principles calculation study of a self-organizing nanostructured lamellar (Ti,Zr)C powder has been performed. The nanoindentation measurements reveal that the hardness of the carbide is comparable to the hardest transition metal carbides that have been reported previously. The origin of the super-high hardness is postulated to be due to the inherent bond strength and the large coherency strains that are generated when the carbide demixes within the miscibility gap. The high hardness is maintained at a high level even after 500 h aging treatment at 1300°C. Therefore, it is believed that the new superhard mixed carbide has a high potential in various engineering applications such as in bulk cemented carbide and cermet cutting tools, and in surface coatings.
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| 44. |
- Masood, Ansar, et al.
(författare)
-
A New Class of Materials for Magneto-Optical Applications : Transparent Amorphous Thin Films of Fe-B-Nb and Fe-B-Nb-Y Metallic Glassy Alloys
- 2014
-
Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 50:4, s. 4004005-
-
Tidskriftsartikel (refereegranskat)abstract
- Optically highly transparent, soft magnetic thin films (4-18 nm thick) of Fe-B-Nb- and Fe-B-Nb-Y-based glassy metal targets were grown on quartz substrates by pulsed laser deposition, and their optical and magneto-optical properties were investigated over the visible spectrum (400-700 nm). All the films found to be fully amorphous in structure were continuous with uniform thickness and surface morphology. Their optical transmittance in the range 50%-85% was found to be film thickness dependent over the entire visible regime. The Verdet constant (V) and Faraday rotation angle (theta(f)) for different films (similar to 4-18 nm) investigated as a function of wavelength (lambda) show considerably higher values for the films of Fe-B-Nb-Y alloy as compared with those for Fe-B-Nb films, e. g., the similar to 4 nm film of Fe-B-Nb-Y alloy exhibits V similar to 49 degrees/Oe cm and theta(f)similar to 26 degrees/mu m while it decreased to similar to 29.4 degrees/Oe and similar to 11.8 degrees/mu m, respectively, for the Fe-B-Nb alloy at lambda=611 nm. A linear relationship is found for the wavelength dependence of V and theta(f) for both alloy systems. To the best of our knowledge, these values are considerably higher than those reported for any other magneto-optic material. The films are found to be soft magnetic with a high saturation moment while their magnetic coercivity values increases with thinness of the films. The observed combination of optical and magneto-optical properties of this new class of amorphous metallic films makes them viable for multifunctional magneto-optical applications.
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| 45. |
- Masood, Ansar, 1983-, et al.
(författare)
-
Effect of Ni-substitution on glass forming ability, mechanical, and magnetic properties of FeBNbY bulk metallic glasses
- 2013
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:1, s. 013505-
-
Tidskriftsartikel (refereegranskat)abstract
- We present a method to identify bulk glass forming ability by partial substitution of Fe by Ni in FeBNbY based amorphous alloy ribbons and as a consequence obtain enhanced mechanical and soft magnetic properties of bulk glassy rods of diameter as large as 4.5 mm. A detailed investigation of thermal, mechanical, and magnetic properties of (Fe0.72-x NixB0.24Nb0.04)(95.5)Y-4.5 alloys (with x similar to 0.02, 0.04, 0.06, 0.08, 0.1) was carried out. The supercooled regime (Delta T-x) and other glass forming parameters, e. g., reduced glass transition temperature (T-rg), the gamma (gamma) parameter, etc., were found to be enhanced due to the Ni substitution resulting in improvement of glass forming ability (GFA). The maximum values of such parameters (Delta T-x similar to 94 K, T-rg similar to 0.644, and gamma similar to 0.435) were obtained for the alloy with x similar to 0.06, making it possible to cast cylindrical rods with 4.5 mm diameter for this composition. Nanoindentation studies on glassy rods also point out that (Fe0.66Ni0.06B0.24Nb0.04)(95.5)Y-4.5 alloy exhibit the maximum value of hardness (H similar to 12 GPa) as well as elastic modulus (E similar to 193 GPa) among all of these samples. In addition to these, that particular sample shows the lowest room temperature coercivity (H-c similar to 210 mOe). By annealing at 823 K, H-c can be further reduced to 60 mOe due to its structural relaxation. We attribute the improved soft magnetic and mechanical properties of as-quenched (Fe0.66Ni0.06B0.24Nb0.04)(95.5)Y-4.5 alloy to higher packing density attained due to its large glass forming ability.
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| 46. |
- Masood, Ansar, 1983-, et al.
(författare)
-
Exchange bias in amorphous Fe-B-Nb thin films
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Amorphous thin films of Fe-B-Nb alloy prepared by Pulse Laser Deposition (PLD) have been studied for their magnetic properties. Films of different thicknesses (200-400nm) were cooled from room temperature down to 5K at remnant state of magnetization (MR) and inplane magnetic hysteresis loops were measured at different temperatures (5-300K). At room temperature, soft ferromagnetism was observed while hysteresis loops revealed a shift from origin by giving rise to the exchange bias anisotropy at liquid helium temperatures. The magnitude of this shift, anisotropy, decreased exponentially by increasing temperature and fully disappears at ~30K. The significant shift of the hysteresis loops observed at liquid helium temperatures after cooling from MR and strong irreversibility between zero field cooled (ZFC) and field cooled (FC) magnetization curves probed under different magnetic fields (5-20Oe) reveal the presence of spin-disorder phase, which influences significantly the low temperature behavior in the present amorphous thin films.
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| 47. |
- Masood, A., et al.
(författare)
-
Fabrication and soft magnetic properties of rapidly quenched Co-Fe-B-Si-Nb ultra-thin amorphous ribbons
- 2019
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier B.V.. - 0304-8853 .- 1873-4766. ; 483, s. 54-58
-
Tidskriftsartikel (refereegranskat)abstract
- Ultra-thin soft magnetic amorphous ribbons of Co-Fe-B-Si-Nb alloy were synthesised by a single step rapid-quenching approach to acquire advantage of improved material performance and lower costs over commercial amorphous alloys. The amorphous ribbons of approximately 5.5 µm thicknesses were quenched by a single roller melt spinner in a single-step production process and characterised for their structural and magnetic properties. The disordered atomic structure of amorphous ribbons was confirmed by the X-ray diffraction. A surface morphology study revealed the continuity of ultra-thin ribbons without pores over a large scale. The amorphous alloy showed the ultra-soft magnetic properties in the as-quenched state. The observed thickness dependency of the magnetic properties was attributed to the increased surface roughness and possibly due to a lack of densely packed atomic structure resulting from the extremely high cooling rates experienced by ultra-thin ribbons. We propose that in-situ thinning process of amorphous ribbons significantly reduces the basic material cost and eliminates the need for post-processing steps; hence it provides the opportunity for mass production of high-performance soft magnetic amorphous ribbons at relatively lower costs.
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| 48. |
- Masood, Ansar, et al.
(författare)
-
Fabrication and tuning soft magnetic and magneto-optical properties of BMGs based Fe-B-Nb-Ni transparent thin films, obtained by Pulsed Laser Deposition
- 2014
-
Ingår i: International Journal of Astrobiology. - : Springer Nature. - 1473-5504 .- 1475-3006. ; 1649:4
-
Tidskriftsartikel (refereegranskat)abstract
- We have fabricated by pulse laser deposition very thin (∼5-7 nm) and thick (∼27-408 nm) films of composition Fe66B24Nb4Ni6 on silicon and quartz substrates respectively, and studied their magnetic and magneto-optic properties at room temperature. We find that the thicker films on silicon can be tuned by appropriate thermal annealing to exploit soft magnetic characteristics with low HC, and high MS values. The magnetic hysteretic loops of the as-deposited thicker films on silicon substrates show two interesting characteristics: 1) increase in the coercivity with the film thickness and 2) the onset of a two stage process during the approach to magnetic saturation. The initial in-plane characteristic of the hysteresis loop is followed by a linear anisotropic behavior between remanence and saturation- that changes into square soft-magnetic loops on decreasing the film thickness. By suitable annealing the intrinsic strain disappears at relatively low temperatures (≤200°C); the thicker films can be tailored to exhibit a simple soft-magnetic square loop with low HC. The ∼5-7 nm films deposited on glass are transparent and have been investigated for their magneto-optic properties using Faraday rotation (FR) measurement technique. Very high values of FR in the range 4-20 deg/μm almost linearly dependent on the wavelength of light in the range 405-611 nm are observed. The observed high values of Faraday rotation over a wide range of wavelength of light are useful for the applications as magneto-optic sensors in the UV to visible range.
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| 49. |
- Masood, A., et al.
(författare)
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High-frequency power loss mechanisms in ultra-thin amorphous ribbons
- 2021
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier B.V.. - 0304-8853 .- 1873-4766. ; 519
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Tidskriftsartikel (refereegranskat)abstract
- Soft magnetic amorphous materials with ultra-low power loss are highly desirable for high-frequency drive applications. The present work demonstrates the high-frequency power loss performance and underlying loss mechanisms in ultra-thin amorphous alloys. This is achieved by rapid-quenching amorphous alloys of Co-, CoFe- and Fe-rich systems, investigating their amorphous atomic structure, quantifying the saturation magnetostriction constants (λs), imaging magnetic domains at remanent magnetization, analyzing magnetization reversal from various magnetization levels, and finally, investigating the material loss performance over a broad frequency range (f = 50 kHz–2 MHz) at various excitation levels (Bm = 25–100 mT). The ultra-high performance of ultra-thin Co-rich amorphous ribbons, as compared to CoFe- and Fe-rich alloys, was attributed to the significantly low eddy current loss, due to the reduced thickness, and a minimal amount of excess loss, owning to minimal magnetoelastic contributions and magnetization reversal by rotation. The underlying loss mechanisms were analyzed by decomposing material loss into primary components and identifying the magnetization reversal mechanisms using minor hysteresis loops. In the Co-rich amorphous alloys, we suggest that magnetization reversal by rotation dominates, at least at low excitations, while in CoFe- and Fe-rich alloys domain wall displacement prevails and contributes significantly to the excess loss up to the MHz frequency range. Magnetization reversal by rotation in Co-rich alloys could be attributed to the zero/near-zero λs, and eventually low residual stress, leading to a homogeneous magnetic domain structure, as compared to the inhomogeneous “fingerprint-like” complex domains in highly magnetostrictive CoFe-rich alloys.
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- Masood, Ansar, 1983-, et al.
(författare)
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Low temperature magnetic hardening in nanocrystalline Fe-Ni-B-Nb thin films
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Low temperature magnetic properties of nanocrystalline FeNiBNb thin films grown by Pulse Laser Deposition (PLD) were investigated. Temperature dependence of magnetization M (T) revealed that weak ferromagnetic amorphous matrix gets magnetically order/disorder and as a consequence, system inters into different state of magnetization by giving rise to interesting global magnetic behaviors. Sample exhibits threefold coercive behavior with the evolution of temperature (5-300K). Magnetic hardening was observed below 25K and attributed to evolution of spin-glass like state of the system.
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