Electrical and optical control of magnetization are of central importance in the research and applications of spintronics. Non-relativistic angular momentum transfer or relativistic spin-orbit ...coupling provide efficient means by which electrical current driven through a ferromagnet can exert a torque on the magnetization. Ferromagnetic semiconductors like (Ga,Mn)As are suitable model systems with which to search for optical counterparts of these phenomena, where photocarriers excited by a laser pulse exert torque upon magnetization. Here, we report the observation of an optical spin-orbit torque (OSOT) in (Ga,Mn)As. The phenomenon originates from spin-orbit coupling of non-equilibrium photocarriers excitated by helicity-independent pump laser pulses, which do not impart angular momentum. In our measurements of the time-dependent magnetization trajectories, the signatures of OSOT are clearly distinct from the competing thermal excitation mechanism, and OSOT can even dominate in (Ga,Mn)As materials with appropriately controlled micromagnetic parameters.
We model changes of magnetic ordering in Mn-based antiperovskite nitrides driven by biaxial lattice strain at zero and at finite temperature. We employ a noncollinear spin-polarized density ...functional theory to compare the response of the geometrically frustrated exchange interactions to a tetragonal symmetry breaking (the so called piezomagnetic effect) across a range of Mn3 AN (A = Rh, Pd, Ag, Co, Ni, Zn, Ga, In, Sn) at zero temperature. Building on the robustness of the effect we focus on Mn3 GaN and extend our study to finite temperature using the disordered local moment (DLM) first-principles electronic structure theory to model the interplay between the ordering of Mn magnetic moments and itinerant electron states. We discover a rich temperature-strain magnetic phase diagram with two previously unreported phases stabilized by strains larger than 0.75% and with transition temperatures strongly dependent on strain. We propose an elastocaloric cooling cycle crossing two of the available phase transitions to achieve simultaneously a large isothermal entropy change (due to the first-order transition) and a large adiabatic temperature change (due to the second-order transition).
We theoretically investigate the tunneling anisotropic magneto-Seebeck effect in a realistically modeled CoPt/MgO/Pt tunnel junction using coherent transport calculations. For comparison we study the ...tunneling magneto-Seebeck effect in CoPt/MgO/CoPt as well. We find that the magneto-Seebeck ratio of CoPt/MgO/Pt exceeds that of CoPt/MgO/CoPt for small barrier widths, reaching 175% at room temperature. This provides a sharp contrast to the magnetoresistance, in which CoPt/MgO/CoPt performs better by one order of magnitude for all barrier widths. Thus, by switching from two ferromagnetic layers to one (so that spin-orbit coupling alone governs the magnetic transport anisotropy), the magnetoresistance ratio diminishes while the magneto-Seebeck ratio remains comparable or improves considerably. We therefore demonstrate that magnetic tunability can increase when caused solely by spin-orbit coupling. This result sheds light on the role that spin-orbit coupling plays in magnetically tuning the properties of tunnel junctions.
An empirical multiorbital (spd) tight binding (TB) model including magnetism and spin–orbit coupling is applied to calculations of magnetic anisotropy energy (MAE) in CoPt L10 structure. A realistic ...Slater–Koster parametrisation for single-element transition metals is adapted for the ordered binary alloy. Spin magnetic moment and density of states are calculated using a full-potential linearised augmented plane-wave (LAPW) ab initio method and our TB code with different variants of the interatomic parameters. Detailed mutual comparison of this data allows for determination of a subset of the compound TB parameters tuning of which improves the agreement of the TB and LAPW results. MAE calculated as a function of band filling using the refined parameters is in broad agreement with ab initio data for all valence states and in quantitative agreement with ab initio and experimental data for the natural band filling. Our work provides a practical basis for further studies of relativistic magnetotransport anisotropies by means of local Green's function formalism which is directly compatible with our TB approach.
•Calculations of electronic structure properties of bulk ordered CoPt alloy using tight-binding (TB) and density functional theory (DFT) approach.•Refinement of existing single-element TB parameters for a binary alloy based on a comparison of band structure and spin magnetic moment per atom to DFT results.•Quantitative agreement of magnetic anisotropy energy (MAE) obtained by TB and DFT on a range of band fillings.•Successful description of ground state spin–orbit coupling phenomena using an extended TB model suitable for subsequent magnetotransport simulations.
We report experimental and theoretical studies of magnetic domain walls in an in-plane magnetized (Ga,Mn)As dilute moment ferromagnetic semiconductor. Our high-resolution electron holography ...technique provides direct images of domain wall magnetization profiles. The experiments are interpreted based on microscopic calculations of the micromagnetic parameters and Landau-Lifshitz-Gilbert simulations. We find that the competition of uniaxial and biaxial magnetocrystalline anisotropies in the film is directly reflected in orientation dependent wall widths, ranging from approximately 40 to 120 nm. The domain walls are of the Néel type and evolve from near-90 degrees walls at low temperatures to large angle 11over 0-oriented walls and small angle 110-oriented walls at higher temperatures.
PDF
