| 1. |
- Aad, G, et al.
(författare)
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- 2015
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swepub:Mat__t
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| 2. |
- Carvalho, P. C., et al.
(författare)
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Complex magnetic textures in Ni/Ir-n/Pt(111) ultrathin films
- 2021
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Ingår i: Physical Review Materials. - : American Physical Society. - 2475-9953. ; 5:12
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Tidskriftsartikel (refereegranskat)abstract
- A combined approach using first-principles calculations and spin dynamics simulations is applied to study Ni/Ir-n/Pt(111) (n = 0, 1, 2) films. The lowest-energy states are predicted to be spin spirals but with a minute (of the order of a few mu eV/atom) energy difference with skyrmionic states. The spontaneous low-temperature skyrmions, with similar to 15 nm to similar to 35 nm size, arise from a large Dzyaloshinskii-Moriya (DM) and Heisenberg exchange interactions ratio and, in particular, from a large in-plane DM vector component for nearest neighbors. The skyrmions become larger and more dispersed with the enhancement of the Ir buffer thickness. Also, with increasing n, the skyrmions' stability decreases when an external magnetic field is applied or the temperature is raised. For n = 0 and n = 1, we find that metastable skyrmioniums can occur, which are characterized by a slightly lower stability with respect to the external fields and larger critical currents, compared to skyrmions.
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| 3. |
- Igarashi, R. N., et al.
(författare)
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First-principles studies of complex magnetism in Mn nanostructures on the Fe(001) surface
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 85:1, s. 014436-
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of Mn nanostructures on the Fe(001) surface have been studied using the noncollinear first-principles real space-linear muffin-tin orbital-atomic sphere approximation method within density-functional theory. We have considered a variety of nanostructures such as adsorbed wires, pyramids, and flat and intermixed clusters of sizes varying from two to nine atoms. Our calculations of interatomic exchange interactions reveal the long-range nature of exchange interactions between Mn-Mn and Mn-Fe atoms. We have found that the strong dependence of these interactions on the local environment, the magnetic frustration, and the effect of spin-orbit coupling lead to the possibility of realizing complex noncollinear magnetic structures such as helical spin spiral and half-skyrmion.
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| 4. |
- Igarashi, R. N., et al.
(författare)
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Magnetic properties of FexCo1-x nanochains on Pt(111) surfaces
- 2014
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 26:20, s. 206003-
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of FexCo1-x nanochains on Pt(1 1 1) were studied using the first-principles real-space linear muffin-tin orbital-atomic sphere approximation (RS-LMTO-ASA) method within the density functional theory. The relative amounts of Fe and Co atoms in a chosen nanochain were varied and several possible arrangements of the atomic species were taken into account. The results of the exchange interaction demonstrates ferromagnetic coupling for the nanowires. Our calculations of Fe and Co average magnetic moments reveal a large enhancement of both spin and orbital moments compared to Fe-Co films deposited on a Pt(1 1 1) surface. The trend for the orbital moments with respect to stoichiometry differs from all previous higher-dimensional Fe-Co alloys on Pt(1 1 1) studies.
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| 5. |
- Miranda, Ivan P., et al.
(författare)
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Band filling effects on the emergence of magnetic skyrmions : Pd/Fe and Pd/Co bilayers on Ir(111)
- 2022
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 105:22
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Tidskriftsartikel (refereegranskat)abstract
- Structurally similar transition metal systems can have widely differing magnetic properties. A prime example of this is found for bilayers on Ir(111), where the Pd/Fe/Ir(111) ground state has a well-established noncollinear spin texture, while Pd/Co/Ir(111) presents a ferromagnetic (FM) single domain. To unravel the origins of these different magnetic behaviors, an investigation of Pd/Fe and Pd/Co bilayers on Ir(111) is here performed. Based on the obtained ab initio electronic structure, exchange coupling parameters Ji j,and Dzyaloshinskii-Moriya interactions (DMIs), we demonstrate that, although in Pd/Co/Ir(111) the DMI is significant, two ingredients play a key role in the origin of noncollinearity in Pd/Fe/Ir(111): the presence of magnetic frustrations and a much more in-plane DMI, both with a long-range influence. The Jij and DMI behaviors in both systems can be explained in terms of a simple rigid-band-like model. Also, by performing spin-dynamics simulations with the magnetic parameters tuned from the Pd/Co/Ir(111) to Pd/Fe/Ir(111) ab initio values, we could find conditions for the emergence of skyrmionic phases in the originally FM Pd/Co/Ir(111).
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| 6. |
- Miranda, I. P., et al.
(författare)
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Mechanisms behind large Gilbert damping anisotropies
- 2021
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:22
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Tidskriftsartikel (refereegranskat)abstract
- A method with which to calculate the Gilbert damping parameter from a real-space electronic structure method is reported here. The anisotropy of the Gilbert damping with respect to the magnetic moment direction and local chemical environment is calculated for bulk and surfaces of Fe50Co50 alloys from first-principles electronic structure in a real-space formulation. The size of the damping anisotropy for Fe50Co50 alloys is demonstrated to be significant. Depending on details of the simulations, it reaches a maximum-minimum damping ratio as high as 200%. Several microscopic origins of the strongly enhanced Gilbert damping anisotropy have been examined, where in particular interface/surface effects stand out, as do local distortions of the crystal structure. Although theory does not reproduce the experimentally reported high ratio of 400% [Phys. Rev. Lett. 122, 117203 (2019)], it nevertheless identifies microscopic mechanisms that can lead to huge damping anisotropies.
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| 7. |
- Rocha-Rodrigues, P., et al.
(författare)
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Probing Ca 3 Ti 2 O 7 crystal structure at the atomic level : Insights from perturbed angular correlation spectroscopy and ab initio studies
- 2024
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 109:22
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Tidskriftsartikel (refereegranskat)abstract
- Perturbed angular correlation spectroscopy combined with ab initio electronic structure calculations is used to unravel the structural phase transition path from the low -temperature polar structure to the high -temperature structural phase in Ca 3 Ti 2 O 7 , a hybrid improper ferroelectric. The experimental procedure, conducted at ISOLDE, explores the unique features of a local probe environment approach by monitoring the evolution of the electric field gradient tensor at the calcium sites. The local environments, observed above 1057 K, confirm a structural phase transition from the A 2 1 am symmetry to an orthorhombic Acaa symmetry in the Ca 3 Ti 2 O 7 crystal lattice, disagreeing with the frequently reported avalanche structural transition from the polar A 2 1 am phase to the aristotype I 4 / mmm phase. Moreover, the EFG temperature dependency, within the A 2 1 am temperature stability, is shown to be sensitive to the recently proposed Ca 3 Ti 2 O 7 ferroelectric polarization decrease within the 500-800 K temperature range.
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| 8. |
- Sousa, O. M., et al.
(författare)
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Charging behavior of ZnMn2O4 and LiMn2O4 in a zinc- and lithium-ion battery : an ab initio study
- 2024
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 2515-7655. ; 6:2
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Tidskriftsartikel (refereegranskat)abstract
- In the field of sustainable energy storage systems, zinc-ion batteries (ZIB) employing aqueous electrolytes have emerged as viable successors to the widely used lithium-ion batteries, attributed to their cost-effectiveness, environmental friendliness, and intrinsic safety features. Despite these advantages, the performance of ZIBs is significantly hindered by the scarcity of suitable cathode materials, positioning manganese zinc oxide (ZnMn2O4) as a potential solution. In this study, we describe the ZnMn2O4 (ZMO) compound focusing on its properties variations during Zn extraction and potential battery applications. For the sake of comparison, we also analyze the same properties of the LiMn2O4 in its tetragonal phase (TLMO), for the first time, motivated by a recent discovery that the substitution of Zn ions by Li in ZMO forms isostructural TLMO compound at room temperature. The study was conducted within the density functional theory (DFT) framework, where the structural, electronic, magnetic, electrochemical, and spectroscopic properties of ZMO and TLMO are investigated under various conditions. Although both systems crystallize in tetragonal structures, they demonstrate distinct electronic and magnetic properties due to different oxidation states of the Mn. Computationally optimized lattice parameters align closely with experimental values. The TLMO exhibits a narrower band gap compared to ZMO, indicating enhanced electrical conductivity. In addition, TLMO presented a lower diffusion energy barrier than ZMO, indicating better ionic conductivity. To evaluate the potential application of these materials in battery technologies, we further explored their volume changes during charging/discharging cycles, simulating Zn or Li ions extraction. TLMO underwent a significant volume contraction of 5.8% upon complete Li removal, while ZMO experienced a more pronounced contraction of 12.5% with full Zn removal. By adjusting ion extraction levels, it is possible to reduce these contractions, thereby approaching more viable battery applications. Voltage profiles, constructed from DFT-based simulation results, unveiled an average voltage of 4.05 V for TLMO, closely matching experimental values. Furthermore, spectroscopy results provide insights into the electronic transitions and validate the computational findings, consolidating our understanding of the intrinsic properties of ZMO and TLMO.
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| 9. |
- Sousa, O. M., et al.
(författare)
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Pressure effect on the structural, electronic, and magnetic properties of the battery cathode material LiMn2O4 : An ab-initio study
- 2023
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Ingår i: Journal of Physics and Chemistry of Solids. - : Elsevier. - 0022-3697 .- 1879-2553. ; 175
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Tidskriftsartikel (refereegranskat)abstract
- LiMn2O4 is a battery cathode material with desirable properties such as low cost, low toxicity, high natural abundance of Mn, and environmental compatibility. By means of first-principles calculations, we study the structural, magnetic, and electronic properties of LiMn2O4 under ambient conditions and high hydrostatic pressures (until 20 GPa). We obtain two oxidation states for Mn, even using a cubic structure, which differ in all analyzed properties: structural, electronic, and magnetic. At P > 0, such properties were found to display a standard behavior decreasing smoothly and linearly with pressure. Furthermore, the enthalpy of cubic and orthorhombic structures under low and high-pressure conditions were examined, showing that no cubic to orthorhombic phase transition exists in all the investigated pressure range, nor is a magnetic cubic to a non-magnetic cubic phase transition possible.
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