| 1. |
- Bergman, Anders, et al.
(författare)
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Ultrafast switching in a synthetic antiferromagnetic magnetic random-access memory device
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:22
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of a synthetic antiferromagnet (a metallic trilayer) have been explored and are shown to exhibit ultrafast switching on a time scale of tens of ps. This conclusion is based on first-principles, atomistic spin dynamics simulations. The simulations are performed at finite temperature, as well as at T = 0 K (the macrospin limit), and we observe a marked temperature dependence of the switching phenomenon. It is shown that, to reach very high switching speeds, it is important that the two ferromagnetic components of the synthetic antiferromagnet have oppositely directed external fields to one another. Then a complex collaboration between precession switching of an internal exchange field and the damping switching of the external field occurs, which considerably accelerates the magnetization dynamics. We discuss a possible application of this fast switching as a magnetic random access memory device, which has as a key component intrinsic antiferromagnetic couplings and an applied Oersted field.
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| 2. |
- Borlenghi, Simone, et al.
(författare)
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Thermomagnonic diode : Rectification of energy and magnetization currents
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:5, s. 054428-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the dynamics of two coupled macrospins connected to thermal baths at different temperatures. The system behaves like a diode which allows the propagation of energy and magnetization currents in one direction only. This effect is described by a simple model of two coupled nonlinear oscillators interacting with two independent reservoirs. It is shown that the rectification phenomenon can be interpreted as a a stochastic phase synchronization of the two spin oscillators. A brief comparison with realistic micromagnetic simulations is presented. This new effect yields promising opportunities in spin caloritronics and nanophononic devices.
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| 3. |
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| 4. |
- Chico, Jonathan, et al.
(författare)
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Thermally driven domain-wall motion in Fe on W(110)
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:1
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Tidskriftsartikel (refereegranskat)abstract
- It has recently been shown that domain walls (DWs) in ferromagnets can be moved in the presence of thermal gradients. In this work we study the motion of narrow domain walls in low-dimensional systems when subjected to thermal gradients. The system chosen is a monolayer of Fe on W(110) which is known to exhibit a large anisotropy while having a soft exchange, resulting in a very narrow domain wall. The study is performed by means of atomistic spin dynamics simulations coupled to first-principles calculations. By subjecting this system to thermal gradients we observe a temperature-dependent movement of the domain wall. The thermal gradient always makes the domain wall move towards the hotter region of the sample with a velocity proportional to the gradient. Our material specific study is complemented by model simulations to discern the interplay between the thermal gradient, magnetic anisotropy, and the exchange interaction and shows that the larger DW velocities are found for materials with broader domain-wall width. The relatively slow DW motion of the Fe/W(110) system is hence primarily caused by its narrow domain-wall width, which results from its large magnetic anisotropy and soft exchange.
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| 5. |
- Delin, Anna, et al.
(författare)
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Excitation spectra and ground-state properties from density-functional theory for the inverted band-structure systems beta-HgS, HgSe, and HgTe
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:3
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Tidskriftsartikel (refereegranskat)abstract
- We have performed a systematic density-functional study of the mercury chalcogenide compounds beta-HgS, HgSe, and HgTe using an all-electron full-potential linear muffin-tin orbital method. We find that, in the zinc-blende structure, both HgSe and HgTe are semimetals whereas beta-HgS has a small spin-orbit-induced band gap. Our calculated relativistic photoemission and inverse photoemission spectra reproduce very well the most recently measured spectra, as do also our theoretical optical spectra. In contrast to the normal situation, we find that the local density approximation to the density functional gives calculated equilibrium volumes in much better agreement with experiment than does the generalized gradient corrected functional. We also address the problem of treating relativistic p electrons with methods based on a scalar-relativistic basis set and show that the effect is rather small for the present systems.
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| 6. |
- Delin, Anna
(författare)
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First-principles calculations of the II-VI semiconductor beta-HgS : Metal or semiconductor
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 65:15
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Tidskriftsartikel (refereegranskat)abstract
- Relativistic all-electron full-potential first-principles calculations have been performed in order to study the symmetry of the energy levels around the valence band maximum in the zinc blende II-VI semiconductors beta-HgS, HgSe, and HgTe. It is demonstrated that in general, an inverted band-structure does not necessarily lead to a zero fundamental energy gap for systems with zinc blende symmetry. Specifically, beta-HgS is found to have at the same time an inverted band structure, and a small, slightly indirect, fundamental energy gap. Possibly, the energy levels around the valence band maximum order differently in each of these systems.
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| 7. |
- Dürrenfeld, Philipp, et al.
(författare)
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Tunable damping, saturation magnetization, and exchange stiffness of half-Heusler NiMnSb thin films
- 2015
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Ingår i: Physical Review B. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 92:21
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Tidskriftsartikel (refereegranskat)abstract
- The half-metallic half-Heusler alloy NiMnSb is a promising candidate for applications in spintronic devices due to its low magnetic damping and its rich anisotropies. Here we use ferromagnetic resonance (FMR) measurements and calculations from first principles to investigate how the composition of the epitaxially grown NiMnSb influences the magnetodynamic properties of saturation magnetization M-S, Gilbert damping alpha, and exchange stiffness A. M-S and A are shown to have a maximum for stoichiometric composition, while the Gilbert damping is minimum. We find excellent quantitative agreement between theory and experiment for M-S and alpha. The calculated A shows the same trend as the experimental data but has a larger magnitude. In addition to the unique in-plane anisotropy of the material, these tunabilities of the magnetodynamic properties can be taken advantage of when employing NiMnSb films in magnonic devices.
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| 8. |
- Kanchana, V., et al.
(författare)
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Electronic structure and x-ray magnetic circular dichroism of Sr2FeMoO6 : Ab initio calculations
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:22
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical investigations of the electronic structure, x-ray absorption, and x-ray magnetic circular dichroism (XMCD) at the Fe L-2,L-3 and Mo L-2,L-3 edges of Sr2FeMoO6 are carried out by means of the generalized gradient approximation. The magnetic coupling between Fe and Mo is found to be antiparallel, which gives direct confirmation of ferrimagnetic ordering and settles controversies existing between the earlier experimental reports. This is also confirmed by our good agreement of the Mo L-2,L-3 edges with experiment. Using our theoretical spectra, we recalculate the spin and orbital magnetic moments by means of the XMCD sum rules and compare the results with a direct self-consistent calculation and experiment.
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| 9. |
- Keshavarz, Samara, et al.
(författare)
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Layer-resolved magnetic exchange interactions of surfaces of late 3d elements : Effects of electronic correlations
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 92:16
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of an ab initio study of the magnetic properties of Fe, Co, and Ni surfaces. In particular, we discuss their electronic structure and magnetic exchange interactions (J(ij)), as obtained bymeans of a combination of density functional theory and dynamical mean-field theory. All studied systems have a pronounced tendency to ferromagnetism both for bulk and surface atoms. The presence of narrowband surface states is shown to enhance the magnetic moment as well as the exchange couplings. The most interesting results were obtained for the Fe surface where the atoms have a tendency to couple antiferromagnetically with each other. This interaction is relatively small when compared to interlayer ferromagnetic interaction, and it depends strongly on the lattice parameter. Local correlation effects are shown to lead to strong changes of the overall shape of the spectral functions. However, they seem not to play a decisive role in the overall picture of magnetic couplings studied here. We have also investigated the influence of correlations on the spin and orbital moments of bulklike and surface atoms. We found that dynamical correlations in general lead to enhanced values of the orbital moment.
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| 10. |
- Krockenberger, Y., et al.
(författare)
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Sr2CrOsO6 : End point of a spin-polarized metal-insulator transition by 5d band filling
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:2, s. 020404-
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Tidskriftsartikel (refereegranskat)abstract
- In the search for new spintronic materials with high spin polarization at room temperature, we have synthesized an osmium-based double perovskite with a Curie temperature of 725 K. Our combined experimental results confirm the existence of a sizable induced magnetic moment at the Os site, supported by band-structure calculations, in agreement with a proposed kinetic-energy-driven mechanism of ferrimagnetism in these compounds. The intriguing property of Sr2 CrOs O6 is that it is at the end point of a metal-insulator transition due to 5d band filling and at the same time ferrimagnetism and high-spin polarization are preserved.
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