| 1. |
- Carvalho de Melo Rodrigues, Debora, et al.
(författare)
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Prediction of a Larger Local Magnetic Anisotropy in Permalloy
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- By means of relativistic, first principles calculations, we investigate the microscopic origin of the vanishingly low magnetic anisotropy of Permalloy. Analyzing the local magnetic anisotropy of these alloys, we find that it can be several orders of magnitude larger than that of the bulk sample, and at least one order of magnitude larger than that of Fe or Ni. We discuss these results in terms of local symmetries of the alloy, and point out that an analysis based on perturbation theory has the spin-orbit coupling entering as a second-order term, as opposed to the naively expected fourth order contribution. The relevance for these findings in experiments, e.g. using pump-probe investigations, is discussed, as well as the implications for building effective spin-Hamiltonians of Permalloy.
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| 2. |
- Cedervall, Johan, et al.
(författare)
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Influence of cobalt substitution on the magnetic properties of Fe5PB2
- 2018
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 57:2, s. 777-784
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Tidskriftsartikel (refereegranskat)abstract
- In this study the effects of cobalt substitutions in Fe5PB2 have been studied. An increased cobalt content reduces the magnetic exchange interactions. This has been concluded from a large, linear decrease in both the Curie temperature as well as the saturated magnetic moment. At high cobalt concentrations, cobalt prefers to order at the M(2) position in the crystal structure. A tunable Curie transition like this shows some prerequisites for magnetic cooling applications.The substitutional effects of cobalt in (Fe1–xCox)5PB2 have been studied with respect to crystalline structure and chemical order with X-ray diffraction and Mössbauer spectroscopy. The magnetic properties have been determined from magnetic measurements, and density functional theory calculations have been performed for the magnetic properties of both the end compounds, as well as the chemically disordered intermediate compounds. The crystal structure of (Fe1–xCox)5PB2 is tetragonal (space group I4/mcm) with two different metal sites, with a preference for cobalt atoms in the M(2) position (4c) at higher cobalt contents. The substitution also affects the magnetic properties with a decrease of the Curie temperature (TC) with increasing cobalt content, from 622 to 152 K for Fe5PB2 and (Fe0.3Co0.7)5PB2, respectively. Thus, the Curie temperature is dependent on composition, and it is possible to tune TC to a temperature near room temperature, which is one prerequisite for magnetic cooling materials.
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| 3. |
- Delczeg-Czirjak, Erna K., et al.
(författare)
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Stabilization of the tetragonal distortion of Fe chi Co1-chi alloys by C impurities : A potential new permanent magnet
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:14, s. 144403-
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Tidskriftsartikel (refereegranskat)abstract
- We have analyzed by density functional theory calculations the structural and magnetic properties of Fe-Co alloys doped by carbon. In analogy with the formation of martensite in steels we predict that such a structure also forms for Fe-Co alloys in a wide range of concentrations. These alloys are predicted to have a stable tetragonal distortion, which in turn leads to an enhanced magnetocrystalline anisotropy energy of up to 0.75 MJ/m(3) and a saturated magnetization field of 1.9 T.
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| 4. |
- Edström, Alexander, 1988-, et al.
(författare)
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Curved Magnetism in CrI3
- 2022
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 128:17
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Tidskriftsartikel (refereegranskat)abstract
- Curved magnets attract considerable interest for their unusually rich phase diagram, often encompassing exotic (e.g., topological or chiral) spin states. Micromagnetic simulations are playing a central role in the theoretical understanding of such phenomena; their predictive power, however, rests on the availability of reliable model parameters to describe a given material or nanostructure. Here we demonstrate how noncollinear-spin polarized density-functional theory can be used to determine the flexomagnetic coupling coefficients in real systems. By focusing on monolayer CrI3, we find a crossover as a function of curvature between a magnetization normal to the surface to a cycloidal state, which we rationalize in terms of effective anisotropy and Dzyaloshinskii-Moriya contributions to the magnetic energy. Our results reveal an unexpectedly large impact of spin-orbit interactions on the curvature-induced anisotropy, which we discuss in the context of existing phenomenological models.
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| 5. |
- Edström, Alexander, et al.
(författare)
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Elastic Scattering of Electron Vortex Beams in Magnetic Matter.
- 2016
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 116:12
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Tidskriftsartikel (refereegranskat)abstract
- Elastic scattering of electron vortex beams on magnetic materials leads to a weak magnetic contrast due to Zeeman interaction of orbital angular momentum of the beam with magnetic fields in the sample. The magnetic signal manifests itself as a redistribution of intensity in diffraction patterns due to a change of sign of the orbital angular momentum of the electron vortex beam. While in the atomic resolution regime the magnetic signal is most likely under the detection limits of present transmission electron microscopes, for electron probes with high orbital angular momenta, and correspondingly larger spatial extent, its detection is predicted to be feasible.
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| 6. |
- Edström, Alexander, et al.
(författare)
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Electronic structure and magnetic properties of L1(0) binary alloys
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:1, s. 014402-
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Tidskriftsartikel (refereegranskat)abstract
- We present a systematic study of the magnetic properties of L1(0) binary alloys FeNi, CoNi, MnAl, and MnGa via two different density functional theory approaches. Our calculations show large magnetocrystalline anisotropies in the order 1 MJ/m(3) or higher for CoNi, MnAl, and MnGa, while FeNi shows a somewhat lower value in the range 0.48-0.77 MJ/m(3). Saturation magnetization values of 1.3 MA/m, 1.0 MA/m, 0.8 MA/m, and 0.9 MA/m are obtained for FeNi, CoNi, MnAl, and MnGa, respectively. Curie temperatures are evaluated via Monte Carlo simulations and show T-C = 916 K and T-C = 1130 K for FeNi and CoNi, respectively. For Mn-based compounds Mn-rich off-stoichiometric compositions are found to be important for the stability of a ferro- or ferrimagnetic ground state with T-C greater than 600 K. The effect of substitutional disorder is studied and found to decrease both magnetocrystalline anisotropies and Curie temperatures in FeNi and CoNi.
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| 7. |
- Edström, Anneli M L, et al.
(författare)
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The major bactericidal activity of human seminal plasma is zinc-dependent and derived from fragmentation of the semenogelins.
- 2008
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Ingår i: Journal of immunology. - 1550-6606. ; 181:5, s. 3413-3421
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Tidskriftsartikel (refereegranskat)abstract
- One of the major roles of seminal plasma is to provide antimicrobial protection for the spermatozoa in the female reproductive tract. We found that the bactericidal activity of seminal plasma was highest after resolution of the seminal clot and that this antibacterial activity subsequently became greatly diminished. The antibacterial activity was derived from peptides generated by fragmentation of the semenogelins while the semenogelin holoproteins displayed no antibacterial activity. After ejaculation the semenogelin-derived peptides were fragmented to smaller and smaller fragments over time and thereby lost antibacterial activity. This paralleled the loss of antibacterial activity of whole seminal plasma both in vitro and after sexual intercourse. Moreover, the antibacterial activity of the semenogelin-derived peptides generated in seminal plasma was strictly zinc-dependent both at neutral and low pH. These data provide novel roles for the resolution of seminal clots and for the high zinc concentration in human seminal plasma.
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| 8. |
- Edström, Alexander, et al.
(författare)
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Magnetic Effects in the Paraxial Regime of Elastic Electron Scattering
- 2016
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Ingår i: Physical review B: covering condensed matter and materials physics. - 2469-9950. ; 94:17
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by a recent claim [Phys.Rev.Lett. 116, 127203 ( 2016)] that electron vortex beams can be used to image magnetism at the nanoscale in elastic scattering experiments, using transmission electron microscopy, a comprehensive computational study is performed to study magnetic effects in the paraxial regime of elastic electron scattering in magnetic solids. Magnetic interactions from electron vortex beams, spin polarized electron beams, and beams with phase aberrations are considered, as they pass through ferromagnetic FePt or antiferromagnetic LaMnAsO. The magnetic signals are obtained by comparing the intensity over a disk in the diffraction plane for beams with opposite angular momentum or aberrations. The strongest magnetic signals are obtained from vortex beams with large orbital angular momentum, where relative magnetic signals above 10(-3) are indicated for 10 (h) over bar orbital angular momentum, meaning that relative signals of one percent could be expected with the even larger orbital angular momenta, which have been produced in experimental setups. All results indicate that beams with low acceleration voltage and small convergence angles yield stronger magnetic signals, which is unfortunately problematic for the possibility of high spatial resolution imaging. Nevertheless, under atomic resolution conditions, relative magnetic signals in the order of 10(-4) are demonstrated, corresponding to an increase with one order of magnitude compared to previous work.
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| 9. |
- Edström, Alexander, et al.
(författare)
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Magnetic properties of (Fe1-xCox)(2)B alloys and the effect of doping by 5d elements
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:17
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Tidskriftsartikel (refereegranskat)abstract
- We have explored, computationally and experimentally, the magnetic properties of (Fe1-xCox)(2)B alloys. Calculations provide a good agreement with experiment in terms of the saturation magnetization and the magnetocrystalline anisotropy energy with some difficulty in describing Co2B, for which it is found that both full potential effects and electron correlations treated within dynamical mean field theory are of importance for a correct description. The material exhibits a uniaxial magnetic anisotropy for a range of cobalt concentrations between x = 0.1 and x = 0.5. A simple model for the temperature dependence of magnetic anisotropy suggests that the complicated nonmonotonic behavior is mainly due to variations in the band structure as the exchange splitting is reduced by temperature. Using density functional theory based calculations we have explored the effect of substitutionally doping the transition metal sublattice by the whole range of 5d transition metals and found that doping by Re or W elements should significantly enhance the magnetocrystalline anisotropy energy. Experimentally, W doping did not succeed in enhancing the magnetic anisotropy due to formation of other phases. On the other hand, doping by Ir and Re was successful and resulted in magnetic anisotropies that are in agreement with theoretical predictions. In particular, doping by 2.5 at.% of Re on the Fe/Co site shows a magnetocrystalline anisotropy energy which is increased by 50% compared to its parent (Fe0.7Co0.3)(2)B compound, making this system interesting, for example, in the context of permanent magnet replacement materials or in other areas where a large magnetic anisotropy is of importance.
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| 10. |
- Edström, Alexander, 1988-
(författare)
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Magnetocrystalline anisotropy of Laves phase Fe2Ta1-xWx from first principles : Effect of 3d-5d hybridization
- 2017
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Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 96:6
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Tidskriftsartikel (refereegranskat)abstract
- ThemaThe magnetic properties of Fe2Ta and Fe2W in the hexagonal Laves phase are computed using density functional theory in the generalized gradient approximation, with the full potential linearized augmented plane-wave method. The alloy Fe2Ta1−xWx is studied using the virtual crystal approximation to treat disorder, with some comparisons to supercell calculations. Fe2Ta is found to be ferromagnetic with a saturation magnetization of μ0Ms=0.66T while, in contrast to earlier computational work, Fe2W is found to be ferrimagnetic with μ0Ms=0.35T. The transition from the ferri- to the ferromagnetic state occurs for x≤0.1. The magnetocrystalline anisotropy energy (MAE) is calculated to 1.25MJ/m3 for Fe2Ta and 0.87MJ/m3 for Fe2W. The MAE is found to be smaller for all values x in Fe2Ta1−xWx than for the end compounds and it is negative (in-plane anisotropy) for 0.1≤x≤0.9. The MAE is carefully analyzed in terms of the electronic structure. Even though there are weak 5d contributions to the density of states at the Fermi energy in both end compounds, a reciprocal space analysis, using the magnetic force theorem, reveals that the MAE originates mainly from regions of the Brillouin zone with strong 3d−5d hybridization near the Fermi energy. Perturbation theory and its applicability in relation to the MAE is discussed.
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