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It is well established that it is possible to switch certain antiferromagnets electrically, yet the interplay of Neel-spin-orbit torques and thermal activation is only poorly understood. Combining ab initio calculations and atomistic spin dynamics simulations we develop a multiscale model to study the current-induced switching in Mn2Au. We compute from first principles the strength and direction of the electrically induced magnetic moments, caused by the Rashba-Edelstein effect, and take these into account in atomistic spin dynamics simulations. Our simulations reveal the switching paths as well as the timescales for switching. The size of the induced moments, however, turns out to be insufficient to lead to fully deterministic switching. Instead, we find that a certain degree of thermal activation is required to help overcome the relevant energy barrier.

Spin-orbit torques (SOTs) have emerged recently as practical tools to control the magnetization in spintronic devices, but it is debated what the underlying fundamental processes are that enable fast and energy-efficient magnetization switching. In this thesis, we investigate theoretically possible means of controlling magnetization in magnetic materials and heterostructures. To this end we employ relativistic density functional theory and linear-response theory to compute electrically induced spin currents and spin polarizations. We focus initially on two effects, the spin Hall effect (SHE) and the spin Rashba-Edelstein effect (SREE) that are due to spin-orbit coupling (SOC). First, we investigate the electric-field induced local magnetization in two antiferromagnets, CuMnAs and Mn2Au. Our explicit calculations show that there is not only an SREE-induced local spin polarization, but also a surprisingly large orbital polarization, due to what we call an orbital Rashba-Edelstein effect (OREE). We show that the induced orbital polarization does not require SOC and that it exhibits a staggered, Rashba symmetry in contrast to the induced spin polarization that can have Rashba- or Dresselhaus-like symmetries. Second, we investigate heavy-metal/ferromagnetic-metal bilayers, previously proposed to be exceptionally suited for large SOTs. Calculating the induced spin currents and accumulations, we find that there is an unusual magnetic spin Hall effect (MSHE), carrying a spin current whose polarization points along the electric field. The MSHE is odd under magnetization reversal, in contrast to the conventional SHE which is magnetization invariant. We investigate further the MSHE for the ferromagnets Fe, Co, and Ni, for which we show that the size of the MSHE can be comparable to that of the SHE and therefore they can in general not be ignored for SOTs. To access their thermal counterparts, we systematically investigate the spin Nernst and orbital Nernst effect (ONE) for 40

Electrical control of magnetization is of crucial importance for integrated spintronics devices. Spin-orbit torques (SOT) in heavy-metal/ferromagnetic heterostructures have emerged as a promising tool to achieve efficiently current-induced magnetization reversal. However, the microscopic origin of the SOT is being debated, with the spin Hall effect (SHE) due to nonlocal spin currents and the spin Rashba-Edelstein effect (SREE) due to local spin polarization at the interface being the primary candidates. We investigate the electrically induced out-of-equilibrium spin and orbital polarizations in pure Pt films and in Pt/3d-metal (Co, Ni, Cu) bilayer films using ab initio electronic structure methods and linear-response theory. We compute atom-resolved response quantities that allow us to identify the induced spin-polarization contributions that lead to fieldlike (FL) SOTs, mostly associated with the SREE, and dampinglike (DL) SOTs, mostly associated with the SHE, and compare their relative magnitude, dependence on the magnetization direction, as well as their Pt-layer thickness dependence. We find that both the FL and DL components contribute to the resulting SOT at the Pt/Co and Pt/Ni interfaces, with the former contributions being larger at the Pt interface layer and the latter larger in the Co or Ni layers. Our calculations show that the electrically induced transverse orbital polarization is exceedingly larger than the induced spin polarization and present even without spin-orbit coupling, in contrast to the spin polarization.

Ever since its first observation, the microscopic origin of ultrafast magnetization dynamics has been actively debated. Even more questions arise when considering composite materials featuring a combination of intrinsic and proximity-induced magnetic moments. Currently, it is unknown whether the specific ultrafast dynamics of different sublattices in the popular ferromagnets consisting of 3d (Co, Fe) and 4d, 5d (Pd, Pt) transition metals are playing a crucial role in various effects, including all-optical magnetization switching. Here we investigate the element-specific dynamics of Co-Pt alloys on femtosecond and picosecond time scales using magneto-optical spectroscopy in the extended ultraviolet (EUV) region. Our results reveal that despite the proximity-induced nature of the magnetization of Pt atoms, the two sublattices in the alloy can have different responses to the optical excitation featuring distinct demagnetization rates. Additionally we show that it is important to consider the modification of magnetic anisotropy in opto-magnetic experiments as the vast majority of them are sensitive only to a single projection of the magnetic moment on the predefined axis, which may lead to experimental artifacts.

We present experimental data and a complete theoretical description of the magneto-optical contributions to the complex refractive index in the extreme ultraviolet (XUV) range covering the 3p resonances of Fe, Co, and Ni. The direct comparison of the two allows us to conclude that many-body corrections to the ground state and local field effects are crucial for an accurate description of M-edge spectra. Our results are relevant for investigation of static magnetization, via XUV spectroscopy of multielement systems, as well as the dynamics of magnetization, as needed in the study of femtomagnetism and spintronics.

Recent outbreaks in bottom-up chemical techniques have demonstrated the synthesis of atomically perfect zigzag graphene nanoribbons (ZGNRs) and of their corresponding analogs with phenyl-edge functionalization [P. Ruffieux et al., Nature 531, 489 (2016)]. Since spin-polarized currents can be generated at the edges of the ZGNRs, the control of phenyl decoration at the zigzag edges could accurately tune the electronic properties of these carbon-based nanoribbons. In the present paper, using first-principles calculations and a Landauer-Buttiker approach, the electronic and magnetic properties as well as the spin-resolved transmissions are investigated in various phenyl-edge-modified ZGNRs. The understanding of the spin-dependent transport properties in relation to the atomic structure opens the way to design devices such as spin valves for future spintronics applications.

Recent outbreaks in bottom-up chemical techniques have demonstrated the synthesis of atomically perfect zigzag graphene nanoribbons (ZGNRs) and of their corresponding analogs with phenyl-edge functionalization [P. Ruffieux et al., Nature 531, 489 (2016)]. Since spin-polarized currents can be generated at the edges of the ZGNRs, the control of phenyl decoration at the zigzag edges could accurately tune the electronic properties of these carbon-based nanoribbons. In the present paper, using first-principles calculations and a Landauer-Büttiker approach, the electronic and magnetic properties as well as the spin-resolved transmissions are investigated in various phenyl-edge-modified ZGNRs. The understanding of the spin-dependent transport properties in relation to the atomic structure opens the way to design devices such as spin valves for future spintronics applications.

The magnetic spin Hall effect (MSHE) is an anomalous charge-to-spin conversion phenomenon which occurs in ferromagnetic materials. In contrast to the conventional spin Hall effect (SHE), being a time-reversal even effect, the magnetic counterpart is time-reversal odd. In this work, we use ab initio calculations to investigate the MSHE for the bulk ferromagnets Fe, Co, and Ni. The magnitudes of the MSHE of Fe and Co are comparable to those of the SHE, but the MSHE is strongly dependent on the electron lifetime and the MSHE and SHE can moreover have opposite signs. For Ni the MSHE is smaller than the SHE, but in general, the MSHE cannot be ignored for spin-orbit torques. Considering a charge current we analyze how both the MSHE and SHE contribute to a total Hall angle. We extend our analysis of the MSHE to its orbital counterpart, that is, the magnetic orbital Hall effect (MOHE), for which we show that the MOHE is in general smaller than the orbital Hall effect (OHE). We compute furthermore the thermal analogs, i.e., the spin and orbital Nernst effects, and their magnetic counterparts. Here our calculations show that the magnetic spin and orbital Nernst effects of Ni are substantially larger than those of Fe and Co.