| 1. |
- Andersson, Mikael S., et al.
(författare)
-
Thermally induced magnetic relaxation in square artificial spin ice
- 2016
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- The properties of natural and artificial assemblies of interacting elements, ranging from Quarks to Galaxies, are at the heart of Physics. The collective response and dynamics of such assemblies are dictated by the intrinsic dynamical properties of the building blocks, the nature of their interactions and topological constraints. Here we report on the relaxation dynamics of the magnetization of artificial assemblies of mesoscopic spins. In our model nano-magnetic system - square artificial spin ice - we are able to control the geometrical arrangement and interaction strength between the magnetically interacting building blocks by means of nano-lithography. Using time resolved magnetometry we show that the relaxation process can be described using the Kohlrausch law and that the extracted temperature dependent relaxation times of the assemblies follow the Vogel-Fulcher law. The results provide insight into the relaxation dynamics of mesoscopic nano-magnetic model systems, with adjustable energy and time scales, and demonstrates that these can serve as an ideal playground for the studies of collective dynamics and relaxations.
|
|
| 2. |
- Arnalds, Unnar B., et al.
(författare)
-
A new look on the two-dimensional Ising model : thermal artificial spins
- 2016
-
Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 18
-
Tidskriftsartikel (refereegranskat)abstract
- We present a direct experimental investigation of the thermal ordering in an artificial analogue of an asymmetric two-dimensional Ising system composed of a rectangular array of nano-fabricated magnetostatically interacting islands. During fabrication and below a critical thickness of the magnetic material the islands are thermally fluctuating and thus the system is able to explore its phase space. Above the critical thickness the islands freeze-in resulting in an arrested thermalized state for the array. Determining the magnetic state we demonstrate a genuine artificial two-dimensional Ising system which can be analyzed in the context of nearest neighbor interactions.
|
|
| 3. |
- Kumar, Ankit, et al.
(författare)
-
Impact of the crystal orientation on spin-orbit torques in Fe/Pd bilayers
- 2020
-
Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 53:35
-
Tidskriftsartikel (refereegranskat)abstract
- Spin-orbit torques in ferromagnetic/non-magnetic heterostructures offer more energy-efficient means to realize spin-logic devices; however, their strengths are determined by the heterostructure interface. This work examines the impact of crystal orientation on the spin-orbit torque efficiency in different Fe/Pd bilayer systems. Results from spin torque ferromagnetic resonance measurements evidence that the damping-like torque efficiency is higher in epitaxial than in polycrystalline bilayer structures while the field-like torque is negligible in all bilayer structures. The strength of the damping-like torque decreases with deterioration of the bilayer epitaxial quality. The present finding provides fresh insight for the enhancement of spin-orbit torques in magnetic heterostructures.
|
|
| 4. |
- Kumar, Ankit, et al.
(författare)
-
Spin transfer torque ferromagnetic resonance induced spin pumping in the Fe/Pd bilayer system
- 2017
-
Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 95:6
-
Tidskriftsartikel (refereegranskat)abstract
- Inconsistencies in estimates of the spin Hall angle (theta(SH)) and spin diffusion length (lambda(SD)) of nonmagnetic (NM) layers using the spin transfer torque ferromagnetic resonance (ST-FMR) in ferromagnetic FM/NM bilayer structures are attributed to the inverse spin Hall effect (ISHE) and interfacial parameter contributions, interface spin transparency, interfacial anisotropic magnetoresistance, and effective spin-mixing conductance. These contributions in Fe(10 nm)/Pd(2-8 nm) bilayer structures have been probed employing the simultaneous detection of ST-FMR and ISHE in conjunction with in-plane FMR measurements. The interfacial contributions are found to increase with an increase in Pd layer thickness (t(NM)), which can be linked to the spin pumping effect in conjunction with spin backflow. Correcting the t(NM) dependence of the ST-FMR spectra for the interfacial and ISHE contributions prior to estimating theta(SH) and theta(SD) of the Pd layer, the estimated values are found to be 0.10 +/- 0.03 and 5.4 +/- 1.2 nm, respectively.
|
|
| 5. |
- Larsen, Simon R., et al.
(författare)
-
Magnetic properties and thermal stability of B2 and bcc phases in AlCoCrFeMnxNi
- 2021
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 861
-
Tidskriftsartikel (refereegranskat)abstract
- Alloys of AlCoCrFeMnxNi (x = 0.0, 0.04, 0.08, 0.12 and 0.16) have been synthesized through arc-melting and gas atomisation (x = 0.0 and 0.16) to investigate the effect of Mn additions to AlCoCrFeNi. Here, the structure, magnetic properties and the thermal stability of the alloys is presented. Electron microscopy confirmed the elemental composition and revealed the microstructure to consist of two spinodally decomposed phases. Rietveld analysis of standard powder X-ray diffraction showed the arc-melted samples consisted of two phases, a B2 phase and a bcc phase while the gas atomised powders consisted of a singlephased B2 structure. Magnetic measurements revealed an increase in the saturation magnetisation at room temperature by 68% for AlCoCrFeMnNi compared to AlCoCrFeNi. The thermal stability of the alloys was investigated using magnetometry, differential scanning calorimetry and in-situ X-ray diffraction, which showed that an increase in Mn content adversely effected the thermal stability of the alloy.
|
|
| 6. |
- Montero Amenedo, José, 1983-, et al.
(författare)
-
Copper-zinc oxide heterojunction catalysts exhibiting enhanced photocatalytic activity prepared by a hybrid deposition method
- 2021
-
Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 11:17, s. 10224-10234
-
Tidskriftsartikel (refereegranskat)abstract
- Heterojunction copper-zinc oxide catalysts were prepared by a hybrid two-step methodology comprising hydrothermal growth of ZnO nanorods (ZnO-NR) followed by deposition of Cu2O nanoparticles using an advanced gas deposition technique (AGD). The obtained bicatalysts were characterized by SEM, AFM, XRD, XPS, PL and spectrophotometry and revealed well-dispersed and crystalline Cu2O nanoparticles attached to the ZnO-NR. The adsorption properties and photocatalytic degradation of Orange II dye in water solutions were measured. It was found that the bicatalysts exhibited a conversion rate and quantum yield that both were about 50% higher compared with ZnO-NR alone, which were attributed to the intrinsic electric field created at the p-n junction formed at the Cu2O/ZnO interface facilitating charge separation of electron-hole pairs formed upon interband photon absorption. The interpretation was evidenced by efficient quenching of characteristic deep level ZnO photoluminescence bands and photoelectron core-level energy shifts. By comparisons with known energy levels in Cu2O and ZnO, the effect was found to be most pronounced for the non-polar ZnO-NR side facets, which accounted for about 95% of the exposed surface area of the catalyst and hence the majority of dye adsorption. It was also found that the dye adsorption capacity of the ZnO nanorods increased considerably after Cu2O deposition thereby facilitating the oxidation of the dye. The results imply the possibility of judiciously aligning band edges on structurally controlled and well-connected low-dimensional semiconductor nanostructures using combined two-step synthesis techniques, where in particular vacuum-based techniques such as AGD allow for growth of well-connected nanocrystals with well developed heterojunction interfaces.
|
|
| 7. |
- Oropesa Nunez, Reinier, et al.
(författare)
-
Insights into the Formation of DNA−Magnetic Nanoparticle Hybrid Structures : Correlations between Morphological Characterization and Output from Magnetic Biosensor Measurement
- 2020
-
Ingår i: ACS Sensors. - : American Chemical Society (ACS). - 2379-3694. ; 5:11, s. 3510-3519
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding the binding mechanism between probe-functionalized magnetic nanoparticles (MNPs) and DNA targets or amplification products thereof is essential in the optimization of magnetic biosensors for the detection of DNA. Herein, the molecular interaction forming hybrid structures upon hybridization between DNA-functionalized magnetic nanoparticles, exhibiting Brownian relaxation, and rolling circle amplification products (DNA-coils) is investigated by the use of atomic force microscopy in a liquid environment and magnetic biosensors measuring the frequency-dependent magnetic response and the frequency-dependent modulation of light transmission. This approach reveals the qualitative and quantitative correlations between the morphological features of the hybrid structures with their magnetic response. The suppression of the high-frequency peak in the magnetic response and the appearance of a new peak at lower frequencies match the formation of larger sized assemblies upon increasing the concentration of DNA-coils. Furthermore, an increase of the DNA-coil concentration induces an increase in the number of MNPs per hybrid structure. This study provides new insights into the DNA-MNP binding mechanism, and its versatility is of considerable importance for the mechanistic characterization of other DNA-nanoparticle biosensor systems.
|
|
| 8. |
- Pohlit, Merlin, et al.
(författare)
-
Collective magnetic dynamics in artificial spin ice probed by ac susceptibility
- 2020
-
Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 101:13
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the study of the thermal dynamics of square artificial spin ice, probed by means of temperatureand frequency-dependent ac susceptibility. Pronounced influence of the interisland coupling strength was found on the frequency response of the samples. Through the subsequent analysis of the frequency- and coupling-dependent freezing temperatures, we discuss the phenomenological parameters obtained in the framework of the Vogel-Fulcher-Tammann law in terms of the samples' microscopic features. The high sensitivity and robust signal to noise ratio of ac susceptibility validate the latter as a promising and simple experimental technique for resolving the dynamics and temperature driven dynamics crossovers for the case of artificial spin ice.
|
|
| 9. |
|
|
| 10. |
- Rani, Parul, et al.
(författare)
-
Rigid Exchange Coupling in Rare-Earth-Lean Amorphous Hard/Soft Nanocomposites
- 2020
-
Ingår i: Advanced Electronic Materials. - : Wiley. - 2199-160X. ; 6:11
-
Tidskriftsartikel (refereegranskat)abstract
- Electrification of vehicles and renewable energy is increasing the demand for permanent magnets, but the cost and scarcity of rare-earth metals is an obstacle. Creating nanocomposites of rigidly exchange-coupled hard and soft magnets, for which the magnetization reversal occurs as in a single magnetic-phase material, is a promising route toward rare-earth-lean permanent magnets with high energy products. The hard/soft exchange coupling is, however, often reduced due to rough interfaces and structural defects, resulting in exchange-spring behavior rather than rigid exchange coupling. Here, it is shown that artificially sandwiched hard and soft amorphous magnets produced by magnetron sputtering exhibit smooth interfaces, and the first order reversal curve (FORC) technique is used to show that the hard and the soft phases are rigidly exchange coupled. Micromagnetic simulations, using a random-anisotropy model, are used to predict the thickness limit of the rigid exchange coupling. A great advantage of amorphous hard/soft composites is the possibility to obtain a wide range of magnetic properties by finely tuning the composition of the individual phases.
|
|
