| 1. |
- Aakash, förnamn, et al.
(författare)
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Structural, magnetic and hyperfine characterizations of nanocrystalline Zn-Cd doped nickel ferrites
- 2017
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Ingår i: Journal of Magnetism and Magnetic Materials. - : ELSEVIER SCIENCE BV. - 0304-8853 .- 1873-4766. ; 441, s. 710-717
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Tidskriftsartikel (refereegranskat)abstract
- In our present work, we have synthesized a series of Cd-Zn doped nickel ferrite ((Cd-0.5 Zn-x(x)) Ni0(.5)Fe(2)O(4); x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) through standard chemical co-precipitation method to study the influence of diamagnetic ions (Cd, Zn) on the magnetic properties of ferrites. XRD and Raman spectroscopy were employed for the structural characterizations. The refinement of the X-ray diffractogram data augmented by the Williamson-Hall plots showed the presence of Cd2+ vacancies and a strained crystal structure. The vibrational spectroscopy indicated the presence of lower space-group symmetry and a distorted crystal structure. Magnetic measurements showed the samples possessed low magnetic anisotropy along with a canted spin structure. The Mossbauer measurements confirmed the cation distribution and gave evidence of super transferred hyperfine interactions arising due to canted spin structure of the system.
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| 2. |
- Ahrentorp, Fredrik, et al.
(författare)
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Effective particle magnetic moment of multi-core particles
- 2015
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 380, s. 221-226
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Tidskriftsartikel (refereegranskat)abstract
- In this study we investigate the magnetic behavior of magnetic multi-core particles and the differences in the magnetic properties of multi-core and single-core nanoparticles and correlate the results with the nanostructure of the different particles as determined from transmission electron microscopy (TEM). We also investigate how the effective particle magnetic moment is coupled to the individual moments of the single-domain nanocrystals by using different measurement techniques: DC magnetometry, AC susceptometry, dynamic light scattering and TEM. We have studied two magnetic multi-core particle systems BNF Starch from Micromod with a median particle diameter of 100 am and FeraSpin R from nanoPET with a median particle diameter of 70 nm - and one single-core particle system - SHP25 from Ocean NanoTech with a median particle core diameter of 25 nm. (C) 2014 Elsevier B.V. All rights reserved.
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| 3. |
- Ahrentorp, Fredrik, et al.
(författare)
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Sensitive magnetic biodetection using magnetic multi-core nanoparticles and RCA coils
- 2017
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 427, s. 14-18
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Tidskriftsartikel (refereegranskat)abstract
- We use functionalized iron oxide magnetic multi-core particles of 100 nm in size (hydrodynamic particle diameter) and AC susceptometry (ACS) methods to measure the binding reactions between the magnetic nanoparticles (MNPs) and bio-analyte products produced from DNA segments using the rolling circle amplification (RCA) method. We use sensitive induction detection techniques in order to measure the ACS response. The DNA is amplified via RCA to generate RCA coils with a specific size that is dependent on the amplification time. After about 75 min of amplification we obtain an average RCA coil diameter of about 1 mu m. We determine a theoretical limit of detection (LOD) in the range of 11 attomole (corresponding to an analyte concentration of 55 fM for a sample volume of 200 mu L) from the ACS dynamic response after the MNPs have bound to the RCA coils and the measured ACS readout noise. We also discuss further possible improvements of the LOD.
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| 4. |
- Akhter, Shahida, et al.
(författare)
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Glassy behavior of diluted Cu-Zn ferrites
- 2018
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Ingår i: Journal of Magnetism and Magnetic Materials. - : ELSEVIER SCIENCE BV. - 0304-8853 .- 1873-4766. ; 452, s. 261-265
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic behavior of Zn substituted Cu-Zn spinel ferrites having chemical formula Cu1-xZnxFe2O4 (x = 0.7, 0.8, 0.9 and 1.0) has been studied by SQUID magnetometry, by means of magnetic hysteresis, field-cooled (FC) and zero-field-cooled (ZFC) magnetization, memory effect and low field ac susceptibility measurements. These measurements suggest that the ferrimagnetic phase of the x <= 0.8 samples is gradually turned into a spin glass (x >= 0.9). The compound with x = 0.9 exhibits the typical dynamical behavior of spin glasses, with indication of aging, rejuvenation and memory effects. The evolution of the magnetic properties of Cu-Zn spinel ferrites with substitution of Zn for Cu is discussed.
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| 5. |
- Al Subhi, A., et al.
(författare)
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Magnetization reversal of antiferromagnetically coupled (Co/Ni) and (Co/Pt) multilayers
- 2019
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 479, s. 27-31
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Tidskriftsartikel (refereegranskat)abstract
- Magnetization reversal and magnetic exchange coupling of (Co/Ni)( x N)/Ru/(Co/Pt)(x12) were investigated as a function of the temperature. The number of repeats N of the soft multilayer (Co/Ni) was varied from 4 to 8 bilayers while the number of repeats of the hard bilayers (Co/Pt) was fixed to 12. Two steps hysteresis loops were observed for coupled structure with only 4 repeats of (Co/Ni) in a wide range of temperature (25-300 K). From the shift of the minor hysteresis loop, the antiferromagnetic exchange coupling H-ex was measured and then the interlayer exchange coupling J(ex) was calculated. A non-monotonous dependence of J(ex) with temperature was observed for N = 4 with a maximum J(ex) of 0.13 erg/cm(2) at 150 K. The annealing process performed on the same structure confirms the unusual behavior of interlayer exchange coupling J(ex). As the repetition number N increases to 8 bilayers the two steps hysteresis loops disappeared in the investigated temperature range, however a small kink appeared in the range of 125 and 225 K for the case of 6 bilayers. From the analysis of the coupled and uncoupled structures, it seems that the dipolar energy overcomes the antiferromagnetic coupling for thicker (Co/Ni) multilayer.
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| 6. |
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| 7. |
- Behera, Nilamani, et al.
(författare)
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Anisotropic magnetic damping studies in β-Ta/2D-epitaxial-Py bilayers
- 2017
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 444, s. 256-262
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Tidskriftsartikel (refereegranskat)abstract
- We report on the anisotropy of the effective damping (αeff) in the sputtered β-Ta(6 nm)/2D-epitaxial-Py(tPy = 3–10 nm) bilayers. In-plane field orientation dependent FMR measurements revealed a prominent anisotropy in αeff, which is ascribed to the spin wave induced spin pumping from Py to β-Ta in β-Ta/epi-Py system. The results especially suggest that at lower tPy a relatively larger αeff and its anisotropic nature are present in β-Ta/epi-Py bilayers as compared to bare epi-Py, which are unlikely at higher tPy. This is possibly due to both spin pumping which stems from in-plane spin waves associated with two magnon scattering mechanism and interface induced anisotropy from heavy metals like β-Ta at β-Ta/Py interface. The in-plane Hr vs. φ reveals clear anisotropy behavior at tPy ≤ 4 nm.
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| 8. |
- Benhouria, Y., et al.
(författare)
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Quantum Monte Carlo study of dynamic magnetic properties of nano-graphene
- 2018
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 460, s. 223-228
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Tidskriftsartikel (refereegranskat)abstract
- Using the Quantum Monte Carlo simulation (QMCS), the dynamic blocking temperature of a nanographene bilayer has been investigated within the framework of the Transverse Ising Model (TIM) with mixed spins, under the existence of the time-dependent oscillating longitudinal magnetic field (h(t) = h(b) + h(0)cos(omega t)) and the transverse field (Omega). The influence of the time-dependent oscillating longitudinal magnetic field, the period of magnetic field (tau) and the transverse field (Omega) on the thermal behavior of the total longitudinal and transverse dynamic order parameters, the total dynamic magnetic susceptibility and the dynamic hysteresis of the nano-graphene bilayer are also studied. As results, we remark the appearance of multiple hysteresis loops and the system exhibits the superparamagnetic behavior at the dynamic blocking temperature.
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| 9. |
- Bouziani, I, et al.
(författare)
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Half metallic ferromagnetic behavior in (Ga, Cr)N and (Ga, Cr, V)N compounds for spintronic technologies : Ab initio and Monte Carlo methods
- 2019
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 477, s. 220-225
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we investigate the magnetic and electronic properties of GaN doped with simple and double impurities utilizing Ab initio and Monte Carlo studies. We have predicted that (Ga, Cr)N and (Ga, Cr, V)N compounds exhibit ferromagnetic- and halfmetallic-behavior with 100% spin polarization at the Fermi level. Moreover, we have found that Ga1-xCrxN and Ga1-2xCrxVxN (x = 0.04, 0.05 and 0.06) show a second order ferromagnetic transition and that their T-c is above room temperature. These predictions make (Ga, Cr)N and (Ga, Cr, V)N compounds strong candidates for spintronic technologies.
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| 10. |
- Bouziani, I., et al.
(författare)
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Magnetoelectronic properties of Vanadium impurities co-doped (Cd, Cr)Te compound for spintronic devices : First principles calculations and Monte Carlo simulation
- 2018
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Ingår i: Journal of Magnetism and Magnetic Materials. - : ELSEVIER SCIENCE BV. - 0304-8853 .- 1873-4766. ; 466, s. 420-429
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Tidskriftsartikel (refereegranskat)abstract
- We have applied the first-principles calculations to investigate magnetoelectronic properties of Vanadium impurities co-doped (Cd, Cr)Te compound for spintronic devices. The ferromagnetic (FM) nature in (Cd, Cr)Te compound co-doped with V atoms has been found, and the mechanism responsible for this behavior has been considered to be the double exchange. Moreover, the Curie-temperature calculation reveals that the stability's field of the FM-phase rises with rising both the concentration of Cr and V atoms above ambient temperature. This system presents the half-metallic character where its polarization of spin is total at the Fermi level, and its total magnetic moment is principally induced by Cr and V elements. The spin-orbit coupling (SOC) typically play an important role in the electronic structure calculations due to both the concentration of Cr and V impurities. In addition to that, our results have been confirmed by the calculation of magnetization and susceptibility using the Monte Carlo simulation.
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| 11. |
- Carrander, Claes, et al.
(författare)
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An application of the time-step topological model for three-phase transformer no-load current calculation considering hysteresis
- 2017
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 423, s. 241-244
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Tidskriftsartikel (refereegranskat)abstract
- In many transformer applications, it is necessary to have a core magnetization model that takes into account both magnetic and electrical effects. This becomes particularly important in three-phase transformers, where the zero-sequence impedance is generally high, and therefore affects the magnetization very strongly. In this paper, we demonstrate a time-step topological simulation method that uses a lumped-element approach to accurately model both the electrical and magnetic circuits. The simulation method is independent of the used hysteresis model. In this paper, a hysteresis model based on the first-order reversal-curve has been used.
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| 12. |
- Cedervall, J., et al.
(författare)
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Magnetic and mechanical effects of Mn substitutions in AlFe 2 B 2
- 2019
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 482, s. 54-60
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical and magnetic properties of the newly discovered MAB-phase class of materials based upon AlFe 2 B 2 were investigated. The samples were synthesised from stoichiometric amounts of all constituent elements. X-ray diffraction shows that the main phase is orthorhombic with an elongated b-axis, similar to AlFe 2 B 2 . The low hardness and visual inspection of the samples after deformation indicate that these compounds are deformed via a delamination process. When substituting iron in AlFe 2 B 2 with manganese, the magnetism in the system goes from being ferro- to antiferromagnetic via a disordered ferrimagnetic phase exhibited by AlFeMnB 2 . Density functional theory calculations indicate a weakening of the magnetic interactions among the transitions metal ions as iron is substituted by manganese in AlFe 2 B 2 . The Mn-Mn exchange interactions in AlMn 2 B 2 are found to be very small.
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| 13. |
- Cedervall, Johan, et al.
(författare)
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Magnetic and mechanical effects of Mn substitutions in AlFe2B2
- 2019
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 482, s. 54-60
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical and magnetic properties of the newly discovered MAB-phase class of materials based upon AlFe2B2 were investigated. The samples were synthesised from stoichiometric amounts of all constituent elements. X-ray diffraction shows that the main phase is orthorhombic with an elongated b-axis, similar to AlFe2B2. The low hardness and visual inspection of the samples after deformation indicate that these compounds are deformed via a delamination process. When substituting iron in AlFe2B2 with manganese, the magnetism in the system goes from being ferro- to antiferromagnetic via a disordered ferrimagnetic phase exhibited by AlFeMnB2. Density functional theory calculations indicate a weakening of the magnetic interactions among the transitions metal ions as iron is substituted by manganese in AlFe2B2. The Mn-Mn exchange interactions in AlMn2B2 are found to be very small.
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| 14. |
- Chakkarapani, Prabu, et al.
(författare)
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Encapsulation of methotrexate loaded magnetic microcapsules for magnetic drug targeting and controlled drug release
- 2015
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 380, s. 285-294
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Tidskriftsartikel (refereegranskat)abstract
- We report on the development and evaluation of methotrexate magnetic microcapsules (MMC) for targeted rheumatoid arthritis therapy. Methotrexate was loaded into CaCO3-PSS (poly (sodium 4-styrenesulfonate)) doped microparticles that were coated successively with poly (allylamine hydrochloride) and poly (sodium 4-styrenesulfonate) by layer-by-layer technique. Ferrofluid was incorporated between the polyelectrolyte layers. CaCO3-PSS core was etched by incubation with EDTA yielding spherical MMC. The MMC were evaluated for various physicochemical, pharmaceutical parameters and magnetic properties. Surface morphology, crystallinity, particle size, zeta potential, encapsulation efficiency, loading capacity, drug release pattern, release kinetics and AC susceptibility studies revealed spherical particles of ~3 µm size were obtained with a net zeta potential of +24.5 mV, 56% encapsulation and 18.6% drug loading capacity, 96% of cumulative drug release obeyed Hixson-Crowell model release kinetics. Drug excipient interaction, surface area, thermal and storage stability studies for the prepared MMC was also evaluated. The developed MMC offer a promising mode of targeted and sustained release drug delivery for rheumatoid arthritis therapy.
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| 15. |
- El Hamri, M., et al.
(författare)
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A theoretical study of the hysteresis behaviors of a transverse spin-1/2 Ising nanocube
- 2016
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 413, s. 30-38
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Tidskriftsartikel (refereegranskat)abstract
- The applied magnetic field dependencies of the surface shell, core and total magnetizations of a transverse spin -I Ising nanocube are investigated within the effective -field theory with correlations, based on the probability distribution technique, for both ferro- and antiferromagnetic exchange interactions. We have found that interfacial coupling has a strong effect on the shape and the number of hysteresis loops and also on the coercive field and remanent magnetization behaviors. Furthermore, when the temperature exceeds a critical one, the coercivities of the core, the surface shell and the system become zero.
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| 16. |
- El Hamri, M., et al.
(författare)
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Reentrant phenomenon in a transverse spin-1 Ising nanoparticle with diluted magnetic sites
- 2017
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 442, s. 53-61
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, we have examined the influence of surface shell exchange coupling on the magnetic properties of a diluted ferromagnetic spin- 1 Ising nanocubic particle, by employing the effective-field theory with correlations based on the probability distribution technique. Some interesting results have been found such as, a tricritical point, a triple point, an isolated critical point, reentrant and even double reentrant phenomena, S-, R- and Q-type behaviors, as well as, both first-and second-order phase transitions as it is confirmed by the free energy. In addition, when the interactions are low between the surface shell sites, quadruple hysteresis loops can be seen in the system.
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| 17. |
- Fazlali, Masoumeh, et al.
(författare)
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Tuning exchange-dominated spin-waves using lateral current spread in nanocontact spin-torque nano-oscillators
- 2019
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 492
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Tidskriftsartikel (refereegranskat)abstract
- We present an efficient method to tailor propagating spin waves in quasi-confined systems. We use nanocontact spin-torque nano-oscillators based on NiFe/Cu/Co spin-valves and study the ferromagnetic and spin-wave resonances (FMR and SWR) of both layers. We employ homodyne-detected ferromagnetic resonance spectroscopy, resembling spin-torque FMR, to detect the magnetodynamics. The external field is applied in-plane, giving a parallel configuration of the magnetic layers, which do not provide any spin-transfer torque. Instead, the excitation is caused by the Oersted field. By varying the thickness of the bottom Cu electrode (t(Cu)) of the devices, we tune the current distribution in the samples, and thereby the Oersted field, which governs the spin wave characteristics. Both the average k-vector and the bandwidth of the SWR increases as t(Cu) increases.
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| 18. |
- Husain, Sajid, et al.
(författare)
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Anomalous Hall effect in ion-beam sputtered Co2FeAl full Heusler alloy thin films
- 2017
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier. - 0304-8853 .- 1873-4766. ; 442, s. 288-294
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Tidskriftsartikel (refereegranskat)abstract
- Investigations of temperature dependent anomalous Hall effect and longitudinal resistivity in Co2FeAl (CFA) thin films grown on Si(1 0 0) at different substrate temperature Ts are reported. The scaling of the anomalous Hall conductivity (AHC) and the associated phenomenological mechanisms (intrinsic and extrinsic) are analyzed vis-à-vis influence of Ts. The intrinsic contribution to AHC is found to be dominating over the extrinsic one. The appearance of a resistivity minimum at low temperature necessitates the inclusion of quantum corrections on account of weak localization and electron-electron scattering effects whose strength reduces with increase in Ts. The study establishes that the optimization of Tsplays an important role in the improvement of atomic ordering which indicates the higher strength of spin-orbit coupling and leads to the dominant intrinsic contribution to AHC in these CFA full Heusler alloy thin films.
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| 19. |
- Husain, Sajid, et al.
(författare)
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Multi-jump magnetization switching in Co2FeAl full Heusler alloy thin films : Experiments and simulations
- 2019
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Ingår i: Journal of Magnetism and Magnetic Materials. - : ELSEVIER SCIENCE BV. - 0304-8853 .- 1873-4766. ; 486
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Tidskriftsartikel (refereegranskat)abstract
- Co2FeAl (CFA) thin films of 50 nm thickness have been grown on MgO (001) single crystal substrates at room temperature with and without post-annealing (PA) at 300 degrees C and 400 degrees C using dual ion-beam sputtering technique. The XRD pattern of the as-grown film revealed that CFA grows with preferred crystallographic orientation on the MgO (001) substrate. Temperature dependent anisotropy measurements on PA films revealed a dominating contribution from cubic anisotropy as confirmed by the analysis of azimuthal angle dependent longitudinal in-plane magneto-optical Kerr effect (MOKE) measurements. The contributions from the cubic and uniaxial anisotropies have also been quantified employing ferromagnetic resonance spectroscopy. Magnetization reversal is accompanied with a plateau in the MOKE hysteresis recorded at various azimuthal angles in the in-plane applied magnetic field configuration. The occurrence of the observed plateau is explained by the presence of a combination of domain walls such as 90 degrees, 135 degrees and 180 degrees domain walls and/or complex domains which is supported by results from micromagnetic simulations. These results demonstrate the feasibility of manipulating the magnetization switching in one of the two ferromagnetic electrodes of the magnetic tunnel junction devices based on Heusler alloy ferromagnetic films.
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| 20. |
- Höglin, Viktor, et al.
(författare)
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Irreversible structure change of the as prepared FeMnP1−xSix-structure on the initial cooling through the curie temperature
- 2015
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 374, s. 455-458
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Tidskriftsartikel (refereegranskat)abstract
- FeMnP0.75Si0.25 experiences a first order para- to ferromagnetic transition at about 200 K. In common with some other alloy compositions crystallizing in the Fe2P structure, the magnetic transition of the as prepared alloy occurs at a lower temperature than on subsequent cooling events. This virgin effect is found to be accompanied by a magnetostrictively induced irreversible structure change that persists on succeeding cooling heating cycles. These findings provide means to understand and control the thermal hysteresis of the (Fe1-xMnx)(2)P1-ySiy alloy system which is a promising material class for use in magnetocaloric refrigerators.
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| 21. |
- Ignakhin, V. S., et al.
(författare)
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Tensile and torsional strain gauge based on Fe48Co32P14B6 metallic glass
- 2019
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Ingår i: Journal of Magnetism and Magnetic Materials. - : ELSEVIER SCIENCE BV. - 0304-8853 .- 1873-4766. ; 476, s. 382-386
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Tidskriftsartikel (refereegranskat)abstract
- We evaluate properties of the prototype of a strain gauge capable to discriminate different strain components: tension and torsion. It makes use of magnetoelastic effect in new Fe48Co32P14B6 metallic glass. As a sensing material, it surpasses characteristics of commercial Iron-Nickel Metglas (R) alloy: relative differential permeability of as quenched amorphous ribbon is of about 110000, the saturation induction B-s = 1.45 T, coercive field as low as 4 A/m, Curie temperature above 700 K, and significantly higher thermal stability. Different deformation components were determined through the analyses of the shape of hysteresis B-H loops. Fe-Co-P-B glass strain gauge can simultaneously detect as small tensile strains as 1.9 x 10(-5) and less than 0.13 deg/cm of torsional distortions.
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| 22. |
- Jonasson, Christian, et al.
(författare)
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Modelling the effect of different core sizes and magnetic interactions inside magnetic nanoparticles on hyperthermia performance
- 2019
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 477, s. 198-202
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Tidskriftsartikel (refereegranskat)abstract
- We present experimental intrinsic loss power (ILP) values, measured at an excitation frequency of 1 MHz and at relatively low field amplitudes of 3.4–9.9 kA/m, as a function of the mean core diameter, for selected magnetic nanoparticles (MNPs). The mean core sizes ranged from ca. 8 nm to 31 nm. Transmission electron microscopy indicated that those with smaller core sizes (less than ca. 22 nm) were single-core MNPs, while those with larger core sizes (ca. 29 nm to 31 nm) were multi-core MNPs. The ILP data showed a peak at core sizes of ca. 20 nm. We show here that this behaviour correlates well with the predicted ILP values obtained using either a non-interacting Debye model, or via dynamic Monte-Carlo simulations, the latter including core-core magnetic interactions for the multi-core particles. This alignment of the models is a consequence of the low field amplitudes used. We also present interesting results showing that the core-core interactions affect the ILP value differently depending on the mean core size.
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| 23. |
- Juszynski, P., et al.
(författare)
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Magnetic anisotropy investigations of (Ga,Mn)As with a large epitaxial strain
- 2015
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 396, s. 48-52
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic properties of 20 nm thick (Ga,Mn)As layer deposited on (Ga,ln)As buffer with very large epitaxial tensile strain are investigated. Gal,In,As buffer with x=30% provides a 2% lattice mismatch, which is an important extension of the mismatch range studied so far (up to 0.5%). Evolution of magnetic anisotropy as a function of temperature is determined by magnetotransport measurements. Additionally, results of direct measurements of magnetization are shown. (C) 2015 Published by Elsevier B.V.
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| 24. |
- Kambhala, Nagaiah, et al.
(författare)
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Study of coexisting phases in Bi doped La0.67Sr0.33MnO3
- 2016
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 406, s. 22-29
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Tidskriftsartikel (refereegranskat)abstract
- We report the remarkable phase separation behavior in La0.67Sr0.33MnO3 doped with Bi3+ ion at La site. The temperature dependent resistivity and magnetization of La0.67-xBixSr0.33MnO3 (x>0) show the presence of phase separation of ferromagnetic metallic and charge ordered antiferromagnetic insulating phases. Markedly, the field dependant magnetization studies of La0.67-xBixSr0.33MnO3 (x=0.3) show the metamagnetic nature of ferromagnetic metallic state implying the competition of coexisting ferromagnetic metallic and charge ordered antiferromagnetic phases. The electron spin resonance and exchange bias studies of La0.67-xBixSr0.33MnO3 (x=0.4 and 0.5) substantiate the coexistence of ferromagnetic clusters in antiferromagnetic matrix.
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| 25. |
- Klaa, Kaltoum, et al.
(författare)
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Composition dependent tuning of electronic and magnetic properties in transition metal substituted Rock-salt MgO
- 2019
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Ingår i: Journal of Magnetism and Magnetic Materials. - : ELSEVIER SCIENCE BV. - 0304-8853 .- 1873-4766. ; 475, s. 44-53
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Tidskriftsartikel (refereegranskat)abstract
- Full potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT) is used to investigate the structural, electronic and magnetic properties of Fe and Ni (3d transition metal) substituted Rock-salt wide band gap insulator Mg1-xMxO (M = Fe, Ni). We have performed spin polarized calculations throughout this work with generalized gradient approximation (GGA) type exchange correlation functional. Additionally, the electronic structures and density of states are computed using modified Becke-Johnson (mBJ) potential based approximation with the inclusion of coulomb energy (U = 7 eV). Based on the Vegard's law and structural optimization, the lattice parameter and bulk modulus are found to be in good agreement with experimental values. Moreover, the analysis of electronic band structures reveals an insulating character for Ni substituted MgO while semiconducting and half-metallic character for Fe substituted case. It has been found that the p-d super-exchange interaction provides a ferromagnetic character due to the 3d transition metal impurities and oxygen atom. The observed p-d hybridization at the top of the valence band edge in this investigations could be useful for magneto-optic and spintronic applications.
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| 26. |
- Kolokoltsev, O., et al.
(författare)
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Compression gain of spin wave signals in a magnonic YIG waveguide with thermal non-uniformity
- 2015
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 377, s. 1-5
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Tidskriftsartikel (refereegranskat)abstract
- We report on the observation of the compression gain of the signals carried by surface spin waves (MSSWs) in yittrium iron garnet films as a result of non-uniform optical heating of the spin wave medium. Efficient gain takes place if a frequency downshift of the spin wave spectrum induced by the heating is compensated by the corresponding non-uniformity of the bias magnetic field. It is proposed that the effect can be understood in part as an interaction between spin waves and a thermally induced potential well in the sample.
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| 27. |
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| 28. |
- Kontos, Sofia, et al.
(författare)
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Measured and calculated properties of B-doped τ-phase MnAl : A rare earth free permanent magnet
- 2019
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 474, s. 591-598
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Tidskriftsartikel (refereegranskat)abstract
- The metastable tetragonal τ-phase MnAl has been doped interstitially with B through a drop synthesis method creating the (Mn0.55Al0.45)B0.02 compound. The as-casted samples were annealed, quenched and thereafter ball-milled and relaxed in order to decrease grain size and reduce the number of crystallographic defects. The Curie temperature of the quenched sample was estimated to 655 K. The magnetization, coercivity and anisotropy were analyzed with respect to flash-milling time, relaxation time and temperature. The results show that (Mn0.55Al0.45)B0.02 could be directly obtained from drop synthesis. The highest measured saturation magnetization of 393 kA/m (measured at ±1440kA/m) was achieved with a relaxation process after 1.5h milling, giving a theoretical maximum energy product of 48 kJ/m3. The highest value of the coercivity was 355 kA/m achieved by flash-milling for 10 h. However, the high coercivity was achieved at an expense of low saturation magnetization.
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| 29. |
- Kwiatkowski, Adam, et al.
(författare)
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Galvanomagnetic methods of Curie temperature determination in (Ga,Mn)As
- 2018
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier. - 0304-8853 .- 1873-4766. ; 467, s. 120-128
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Tidskriftsartikel (refereegranskat)abstract
- We critically discuss various experimental methods to determine Curie temperature T-C of (Ga,Mn)As thin layers or other conducing magnetic materials by means of electric charge transport measurements. They all base on the influence of sample magnetization on the magnetoresistivity tensor <(rho)overcap>and are an alternative to the method based upon an analysis of the temperature derivative of the sample resistance (Novak a al., 2008). These methods can be applied even when standard SQUID magnetometers are difficult or impossible to use - for example for extremely small samples or in the case of experiments performed at very specific physical conditions, e.g. at high hydrostatic pressure inside the clamp cell. We show that the use of the so called Arrott plot prepared with the use of high magnetic field isotherms rho(xx)(H-0), rho(x)y(H-0) (H-0 - external magnetic field) may lead to substantial (of the order of 10 K) divergence of the obtained T-c values depending on the assumptions which are necessary to make in this case and depending on the direction of a magnetic anisotropy easy axis. We also propose a number of ways how to obtain, basing on low magnetic field isotherms rho(xx)(H-0), rho(xy)(H-0) clear and characteristic features which are closely related to the ferromagnetic-paramagnetic phase transition.
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| 30. |
- Liu, J., et al.
(författare)
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Anomalous effects of Sc substitution and processing on magnetism and structure of (Gd1-xScx)(5)Ge-4
- 2019
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 474, s. 482-492
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Tidskriftsartikel (refereegranskat)abstract
- The kinetic arrest observed in the parent Gd5Ge4 gradually vanishes when a small fraction (x = 0.025, 0.05 and 0.10) of Gd is replaced by Sc in (Gd1-xScx)(5)Ge-4, and the magnetic ground state changes from antiferromagnetic (AFM) to ferromagnetic (FM). A first order phase transition coupled with the FM-AFM transition occurs at T-C = 41 K for x = 0.05 and at T-C = 53 K for x = 0.10 during heating in applied magnetic field of 1 kOe, and the thermal hysteresis is near 10 K. The first-order magnetic transition is coupled with the structural Sm5Ge4-type to Gd5Si4-type transformation. The magnetization measured as a function of applied magnetic field shows sharp metamagnetic-like behavior. At the same time, the AFM to paramagnetic transition in (Gd1-xScx)(5)Ge-4 with x = 0.10, is uncharacteristically broad indicating development of strong short-range AFM correlations above the Ned temperature. Comparison of the magnetization data of bulk, powdered, and metal-varnish composite samples of (Gd0.95Sc0.05)(5)Ge-4 shows that mechanical grinding and fabrication of a composite have little effect on the temperature of the first-order transformation, but short-range ordering and AFM/FM ratio below T-C are surprisingly strongly affected.
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| 31. |
- Ludwig, Frank, et al.
(författare)
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Size analysis of single-core magnetic nanoparticles
- 2017
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 427, s. 19-24
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Tidskriftsartikel (refereegranskat)abstract
- Single-core iron-oxide nanoparticles with nominal core diameters of 14 nm and 19 nm were analyzed with a variety of non-magnetic and magnetic analysis techniques, including transmission electron microscopy (TEM), dynamic light scattering (DLS), static magnetization vs. magnetic field (M-H) measurements, ac susceptibility (ACS) and magnetorelaxometry (MRX). From the experimental data, distributions of core and hydrodynamic sizes are derived. Except for TEM where a number-weighted distribution is directly obtained, models have to be applied in order to determine size distributions from the measurand. It was found that the mean core diameters determined from TEM, M-H, ACS and MRX measurements agree well although they are based on different models (Langevin function, Brownian and Néel relaxation times). Especially for the sample with large cores, particle interaction effects come into play, causing agglomerates which were detected in DLS, ACS and MRX measurements. We observed that the number and size of agglomerates can be minimized by sufficiently strong diluting the suspension.
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| 32. |
- Magnuson, Martin
(författare)
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Induced magnetism at the interfaces of a Fe/V superlattice investigated by resonant magnetic x-ray scattering
- 2017
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier. - 0304-8853 .- 1873-4766. ; 422, s. 362-366
-
Tidskriftsartikel (refereegranskat)abstract
- The induced magnetic moments in the V 3d electronic states of interface atomic layers in a Fe(6ML)/V(7ML) superlattice was investigated by x-ray resonant magnetic scattering. The first V atomic layer next to Fe was found to be strongly antiferromagnetically polarized relatively to Fe and the magnetic moments of the next few atomic layers in the interior V region decay exponentially with increasing distance from the interface, while the magnetic moments of the Fe atomic layers largely remain bulk-like. The induced V moments decay more rapidly as observed by x-ray magnetic scattering than in standard x-ray magnetic circular dichroism. The theoretical description of the induced magnetic atomic layer profile in V was found to strongly rely on the interface roughness within the superlattice period. These results provide new insight into interface magnetism by taking advantage of the enhanced depth sensitivity to the magnetic profile over a certain resonant energy bandwidth in the vicinity of the Bragg angles.
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| 33. |
- Masood, A., et al.
(författare)
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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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| 34. |
- Monsen, Asmund, et al.
(författare)
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Point contact investigations of film and interface magnetoresistance of La0.7Sr0.3MnO3 heterostructures on Nb:SrTiO3
- 2015
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 374, s. 433-439
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Tidskriftsartikel (refereegranskat)abstract
- STM based magnetotransport measurements of epitaxial La0.7Sr0.3MnO3 31 nm thick films with and without an internal LaMnO3 layer (0-3.1 nm thick) grown on Nb doped SrTiO3 are presented. The measurements reveal two types of low field magnetoresistance (LFMR) with a magnitude of similar to 0.1-1.5%. One LFMR contribution is identified as a conventional grain boundary/domain wall scattering through the symmetric I-V characteristics, high dependence on tip placements and insensitivity to introduction of LaMnO3 layers. The other contribution originates from the reverse biased Nb doped SrTiO3 interface and the interface layer of La0.7Sr0.3MnO3. Both LFMR contributions display a field dependence indicative of a higher coercivily (similar to 200 Oe) than the bulk film. LaMnO3 layers are found to reduce the rectifying properties of the junctions, and sub micron lateral patterning by electron beam lithography enhances the dioclic properties, in accordance with a proposed transport model based on the locality of the injected current.
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| 35. |
- Prabu, Chakkarapani, et al.
(författare)
-
Layer-by-layer assembled magnetic prednisolone microcapsules (MPC) for controlled and targeted drug release at rheumatoid arthritic joints
- 2017
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 427, s. 258-267
-
Tidskriftsartikel (refereegranskat)abstract
- We report here in about the formulation and evaluation of Magnetic Prednisolone Microcapsules (MPC) developed in order to improve the therapeutic efficacy relatively at a low dose than the conventional dosage formulations by means of magnetic drug targeting and thus enhancing bioavailability at the arthritic joints. Prednisolone was loaded to poly (sodium 4-styrenesulfonate) (PSS) doped calcium carbonate microspheres confirmed by the decrease in surface area from 97.48 m2/g to 12.05 of m2/g by BET analysis. Adsorption with oppositely charged polyelectrolytes incorporated with iron oxide nanoparticles was confirmed through zeta analysis. Removal of calcium carbonate core yielded MPC with particle size of ~3.48 µm, zeta potential of +29.7 mV was evaluated for its magnetic properties. Functional integrity of MPC was confirmed through FT-IR spectrum. Stability studies were performed at 25 °C±65% relative humidity for 60 days showed no considerable changes. Further the encapsulation efficiency of 63%, loading capacity of 18.2% and drug release of 88.3% for 36 h and its kinetics were also reported. The observed results justify the suitability of MPC for possible applications in the magnetic drug targeting for efficient therapy of rheumatoid arthritis.
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| 36. |
- Sarkar, Tapati, et al.
(författare)
-
Thermal evolution of the spin ordering at the concomitant spin-orbital rearrangement temperature in RVO3 (R=Lu, Yb and Tm)
- 2016
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 409, s. 87-91
-
Tidskriftsartikel (refereegranskat)abstract
- Synthesis, crystal structure and magnetization measurements of phase pure polycrystalline RVO3 (R=Lu, Yb and Tm) are reported. The compounds were stabilized in the orthorhombic structure by thermal treatment of the respective precursors (RVO4) in a reducing atmosphere. Special pressure treatment was carried out during the synthesis to ensure phase pure samples without secondary phases. Magnetization measurements reveal the presence of two spin ordering temperatures in the samples. Interestingly, at the lower spin ordering temperature, TsO2, the uncompensated excess moment of the antiferromagnetic spin structure has different field dependences above and below TsO2, causing a jump in the thermal evolution of the magnetization that changes sign with increasing field strength. This jump is associated with the reported magnetic and orbital rearrangement in the samples, and the different spin configurations in the C- and G-type antiferromagnetic structures.
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| 37. |
- Sbiaa, R., et al.
(författare)
-
Ni thickness influence on magnetic properties (Co/Ni/Co/Pt) multilayers with perpendicular magnetic anisotropy
- 2017
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 441, s. 585-589
-
Tidskriftsartikel (refereegranskat)abstract
- We present a study of perpendicular magnetic anisotropy in [Co/Ni(t)/Co/Pt](x8) multilayers for use as free layers in magnetic tunnel junctions (MTJ) and spin valves. The thickness t of the Ni sub-layer was varied and the resulting magnetic properties were investigated. As determined from magnetic force microscopy and magnetometry measurements, all multilayers exhibited a perpendicular magnetic anisotropy with an increase of saturation magnetization with thickness t. From the temperature dependence of the magnetization, well described by a Bloch law, we find that the spin-wave stiffness constant of the [Co/Ni(t)/Co/Pt](x8) multilayers is larger compared to (Co/Ni) multilayers. These multilayers could be the basis for spintronic devices where the reduction of total Pt content could help to reduce the damping constant while keeping the magnetic anisotropy energy relatively high. These are conflicting requirements needed for high performance magnetic memory devices. (C) 2017 Elsevier B.V. All rights reserved.
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| 38. |
- Serantes, David, et al.
(författare)
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Scaling the effect of the dipolar interactions on the ZFC/FC curves of random nanoparticle assemblies
- 2018
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 460, s. 28-33
-
Tidskriftsartikel (refereegranskat)abstract
- Zero field cooling (ZFC) and field cooling (FC) protocols are commonly used to investigate the properties of magnetic nanoparticle systems. For non-interacting conditions the particle properties are fairly well correlated with the shape of the ZFC/FC curves. However, that is not the case when significant dipolar interparticle interactions (DII) are present, which frequently occurs in experimental samples (e.g. aggregates in biological systems; or the dried powder often used for the ZFC/FC measurements). The purpose of this work is to show how the influence of the DII on the ZFC/FC curves, computed by the volume sample concentration c, can be described in a general way if scaled by the dimensionless parameter c(0) = -2K/M-S(2); where K and MS are the anisotropy and saturation magnetization constants of the particles, respectively. This scaling parameter, which is straightforwardly derived from the energy equation governing the system, has an analogous meaning to the normalization of the external magnetic field H by the anisotropy field of the particles HA = 2K/M-S. We use a Monte Carlo technique to illustrate how apparently different T-B vs. c curves of various particles types (where T-B is the blocking temperature), follow the same trend if scaling c/c(0).
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| 39. |
- Singh, Suraj Kumar, et al.
(författare)
-
Effect of oxygen partial pressure on the density of antiphase boundaries in Fe3O4 thin films on Si(100)
- 2018
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 448, s. 303-309
-
Tidskriftsartikel (refereegranskat)abstract
- PoPolycrystalline Fe3O4 thin films were grown on Si(100) substrate by reactive DC sputtering at different oxygen partial pressures PO2" tabindex="0" id="MathJax-Element-3-Frame" class="MathJax_SVG" style="font-size: 90%; display: inline-block; position: relative;"> for controlling the growth associated density of antiphase boundaries (APBs). The micro-Raman analyses were performed to study the structural and electronic properties in these films. The growth linked changes in the APBs density are probed by electron–phonon coupling strength (λ) and isothermal magnetization measurements. The estimated values of λ are found to vary from 0.39 to 0.56 with the increase in PO2" tabindex="0" id="MathJax-Element-4-Frame" class="MathJax_SVG" style="font-size: 90%; display: inline-block; position: relative;"> from 2.2 × 10−5 to 3.0 × 10−5 Torr, respectively. The saturation magnetization (saturation field) values are found to increase (decrease) from 394 (5.9) to 439 (3.0) emu/cm3 (kOe) with the increase in PO2" tabindex="0" id="MathJax-Element-5-Frame" class="MathJax_SVG" style="font-size: 90%; display: inline-block; position: relative;">. The sharp Verwey transition (∼120 K), low saturation field, high saturation magnetization and low value of λ (comparable to the bulk value ∼0.51) clearly affirm the negligible amount of APBs in the high oxygen partial pressure deposited thin films.
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| 40. |
- Sofronova, S., et al.
(författare)
-
Crystal growth, structure, magnetic properties and theoretical exchange interaction calculations of Cu2MnBO5
- 2016
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 420, s. 309-316
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Tidskriftsartikel (refereegranskat)abstract
- Single crystals of ludwigite Cu2MnBO5 were synthesized by flux growth technique. The detailed structural and magnetic characterizations of the synthesized samples have been carried out. The cations composition of the studied crystal was determined using X-ray diffraction and EXAFS technique, the resulting composition differ from the content of the initial Mn2O3–CuO components of the flux. Magnetic susceptibility measurements and the calculations of the exchange integrals in frameworks of indirect coupling model revealed that monoclinic distortions strongly affect exchange interactions and appearance of magnetic ordering phase at the temperature T=93 K. The hypothesis of the existence of several magnetic subsystems was supposed.
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| 41. |
- Sriviriyakul, Thana, et al.
(författare)
-
Nanorheological studies of xanthan/water solutions using magnetic nanoparticles
- 2019
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier B.V.. - 0304-8853 .- 1873-4766. ; 473, s. 268-271
-
Tidskriftsartikel (refereegranskat)abstract
- We show results of nanorheological studies of different concentrations of xanthan (non-Newtonian fluid) in water using magnetic nanoparticles (MNPs) together with the AC susceptibility (ACS) vs frequency method. For comparison we also show the ACS response for different concentrations of glycerol in water (Newtonian fluid). The ACS response is measured, and the data is modelled using dynamic magnetic models and different viscoelastic models. We study the ACS response (in-phase and out-of-phase ACS components) at different concentrations of xanthan in water (up to 1 wt% xanthan) and with a constant concentration of MNPs. We use MNP systems that show Brownian relaxation (sensitive to changes in the environmental properties around the MNPs). ACS measurements are performed using the DynoMag system. The Brownian relaxation of the MNP system peak is shifting down in frequency and the ACS response is broadening and decreases due to changes in the viscoelastic properties around the MNPs in the xanthan solution. The viscosity and the storage moduli are determined at each excitation frequency and compared with traditional macroscopic small amplitude oscillatory shear rheological measurements. The results from the traditional rheological and nanorheological measurements correlate well at higher xanthan concentration.
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| 42. |
- Sun, Li, et al.
(författare)
-
Anomalously large ferromagnetic resonance linewidth in the Gd/Cr/Fe film plane
- 2018
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 451, s. 480-486
-
Tidskriftsartikel (refereegranskat)abstract
- As an important parameter for characterizing the magnetization dynamics, Gilbert damping constant a in a thin film or a multilayer is generally extracted from the linear fitting of the frequency-dependence of the ferromagnetic resonance linewidth, sometimes accompanied with a tiny deviation of the linewidth to a smaller value at the low-frequency or high-frequency region due to the two-magnon scattering with an in-plane-field configuration, in which an in-plane magnetic field H perpendicular to a microwave field h was applied in film plane during measurement. In contrast, here we report, in ultrathin Gd/Cr/Fe multilayers, an anomalously large linewidth in the film plane at the low-frequency region. For the first time, we have successfully extracted the Gilbert damping constant from perfect theoretical fitting to the experimental data, by considering the effective direction of the magnetization around in precession staying out of the film plane when the in-pane H at which the precession starts is below the saturation field. This magnetization deviation from the film plane is found to have an obvious contribution to the enhanced linewidth caused by two magnon scattering, while slightly reduce the intrinsic linewidth. Under the same resonance frequency, the deviation angle reaches the maximum values at t(Cr) = 1.0 nm while decreases when t(Cr) increases to 1.5 nm, which coincides with the trend of the surface perpendicular anisotropy constant K-perpendicular to. A reduced intrinsic damping constant alpha is obtained as the introduction of Gd layer and Cr layer as a result of the competition between the spin pumping effect and the interfacial effects at the Fe/Gd and Fe/Cr interfaces. While the decreasing alpha for film with Cr layer thickness increasing to 1.5 nm might means the contribution of the electron density of states at the Fermi energy n(E-F). This study offers an effective way to accurately obtain the intrinsic damping constant of spintronic materials/devices, which is essential for broad applications in spintronics.
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| 43. |
- Thonig, Danny, 1986-, et al.
(författare)
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Pinning of thermal excitations at defects in artificial dipolar arrays : A theoretical investigation
- 2015
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier. - 0304-8853 .- 1873-4766. ; 386, s. 117-124
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Tidskriftsartikel (refereegranskat)abstract
- In this theoretical investigation we address the effect of defects on thermal excitations in square-lattice dipolar arrays. The samples consist of nanomagnets, whose geometry is adopted from recent experiments [A. Farhan et al.; Nat. Phys. 9 (2013) 375] [13] and allows for thermal activation at room temperature. Various types of defects, all of which may be produced by microstructuring techniques, are introduced into the systems. It turns out that excitations can efficiently be pinned at defects. Furthermore, it is possible to produce ferromagnetic strings of nanomagnets that connect a pair of defects; their lengths are closely related to the distance of the defects and the topology of the magnetic ground-state configuration.
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| 44. |
- Toparli, Cigdem, et al.
(författare)
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Synthesis, structural and magnetic characterization of soft magnetic nanocrystalline ternary FeNiCo particles
- 2017
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 423, s. 133-139
-
Tidskriftsartikel (refereegranskat)abstract
- The present study focuses on the synthesis, microstructural and magnetic properties of ternary FeNiCo nanoparticles. Nanocrystalline ternary FeNiCo particles were synthesized via hydrogen reduction assisted ultrasonic spray pyrolysis method in single step. The effect of precursor concentration on the morphology and the size of particles was investigated. The syntheses were performed at 800 °C. Structure, morphology and magnetic properties of the as-prepared products were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) studies. Scherer calculation revealed that crystallite size of the ternary particles ranged between 36 and 60 nm. SEM and TEM investigations showed that the particle size was strongly influenced by the precursor concentration and Fe, Ni, Co elemental composition of individual particles was homogeneous. Finally, the soft magnetic properties of the particles were observed to be a function of their size.
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| 45. |
- Uzdin, V M, et al.
(författare)
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Energy surface and lifetime of magnetic skyrmions
- 2018
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier. - 0304-8853 .- 1873-4766. ; 459, s. 236-240
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Tidskriftsartikel (refereegranskat)abstract
- The stability of skyrmions in various environments is estimated by analyzing the multidimensional surface describing the energy of the system as a function of the directions of the magnetic moments in the system. The energy is given by a Heisenberg-like Hamiltonian including terms representing Dzyaloshinskii-Moriya interaction, anisotropy energy and interaction with an external magnetic field. Local minima on this surface correspond to the ferromagnetic and skyrmion states. Minimum energy paths (MEP) between the minima are calculated using the geodesic nudged elastic band method. The maximum energy along an MEP corresponds to a first order saddle point on the energy surface and gives an estimate of the activation energy for the magnetic transition, such as creation and annihilation of a skyrmion. The pre-exponential factor in the Arrhenius law for the rate, the so-called attempt frequency, is estimated within harmonic transition state theory where the eigenvalues of the Hessian at the saddle point and the local minima are used to characterize the shape of the energy surface. For some degrees of freedom, so-called “zero modes”, the energy of the system remains invariant. They need to be treated separately and give rise to temperature dependence of the attempt frequency. As an example application of this general theory, the lifetime of a skyrmion in a track of finite width for a PdFe overlayer on a Ir(1 1 1) substrate is calculated as a function of track width and external magnetic field. Also, the effect of non-magnetic impurities is studied. Various MEPs for annihilation inside a track, via the boundary of a track and at an impurity are presented. The attempt frequency as well as the activation energy has been calculated for each mechanism to estimate the transition rate as a function of temperature.
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| 46. |
- Witte, Kerstin, et al.
(författare)
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Particle size- and concentration-dependent separation of magnetic nanoparticles
- 2017
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 427, s. 320-324
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Tidskriftsartikel (refereegranskat)abstract
- Small magnetic nanoparticles with a narrow size distribution are of great interest for several biomedical applications. When the size of the particles decreases, the magnetic moment of the particles decreases. This leads to a significant increase in the separation time by several orders of magnitude. Therefore, in the present study the separation processes of bionized nanoferrites (BNF) with different sizes and concentrations were investigated with the commercial Sepmag Q system. It was found that an increasing initial particle concentration leads to a reduction of the separation time for large nanoparticles due to the higher probability of building chains. Small nanoparticles showed exactly the opposite behavior with rising particle concentration up to 0.1 mg(Fe)/ml. For higher iron concentrations the separation time remains constant and the measured Z-average decreases in the supernatant at same time intervals. At half separation time a high yield with decreasing hydrodynamic diameter of particles can be obtained using higher initial particle concentrations.
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