We study deterministic magnetic reversal of a perpendicularly magnetized Co layer in a Co/MgO/Ta nano-square driven by spin Hall torque from an in-plane current flowing in an underlying Pt layer. The rate-limiting step of the switching process is domain-wall (DW) depinning by spin Hall torque via a thermally-assisted mechanism that eventually produces full reversal by domain expansion. An in-plane applied magnetic field collinear with the current is required, with the necessary field scale set by the need to overcome DW chirality imposed by the Dzyaloshinskii-Moriya interaction. Once Joule heating is taken into account the switching current density is quantitatively consistent with a spin Hall angle θ SH ≈ 0.07 for 4 nm of Pt.  J  Jx , such that the direction of switching is determined by the sign of    J H . 2-4 Here we analyze the microscopic processes in operation during current-driven reversal of PMA samples, and show that for quantitative understanding it is necessary to move beyond a previous macrospin description and consider how the depinning of magnetic domain walls is governed by the combined effects of an in-plane magnetic field and the torque induced by the in-plane current.

Coherent gigahertz-frequency surface acoustic waves (SAWs) traveling on the surface of a piezoelectric crystal can, via the magnetoelastic interaction, resonantly excite traveling surface spin waves in an adjacent thin-film ferromagnet. These excited surface spin waves, traveling with a definite in-plane wavevector q enforced by the SAW, can be detected by measuring changes in the electro-acoustical transmission of a SAW delay line. Here, we provide a demonstration that such measurements constitute a precise and quantitative technique for spin-wave spectroscopy, providing a means to determine both isotropic and anisotropic contributions to the spin-wave dispersion and damping. We demonstrate the effectiveness of this spectroscopic technique by measuring the spin-wave properties of a Ni thin film for a large range of wave vectors, q = 2.5 10 4 -8 10 4 cm -1 , over which anisotropic dipolar interactions vary from being negligible to quite significant.2

Harmonic measurements of the longitudinal and transverse voltages in Bi-Sb/Co bilayers are presented. A large second harmonic voltage signal due to the ordinary Nernst effect is observed. In experiments where a magnetic field is rotated in the film plane, the ordinary Nernst effect shows the same angular dependence in the transverse voltage as the damping-like spin-orbit torque and in the longitudinal voltage as the unidirectional spin-Hall magneto-resistance respectively. Therefore, the ordinary Nernst effect can be a spurious signal in spin-orbit torque measurements, leading to an overestimation of the spin-Hall angle in topological insulators or semimetals. arXiv:1810.05674v1 [cond-mat.mes-hall]

We report measurements of the in-plane magnetoelastic coupling in ultra-thin Ta|CoFeB|MgO layers as a function of uniaxial strain, conducted using a four-point bending apparatus. For annealed samples, we observe a strong dependence on the thickness of the CoFeB layer in the range 1.3-2.0 nm, which can be modeled as arising from a combination of effective surface and volume contributions to the magnetoelastic coupling. We point out that if similar thickness dependence exists for magnetoelastic coupling in response to biaxial strain, then the standard Néel model for the magnetic anisotropy energy acquires a term inversely proportional to the magnetic layer thickness. This contribution can significantly change the overall magnetic anisotropy, and provides a natural explanation for the strongly nonlinear dependence of magnetic anisotropy energy on magnetic layer thickness that is commonly observed for ultrathin annealed CoFeB|MgO films with perpendicular magnetic anisotropy.

The successful operation of spin-based data storage devices depends on thermally stable magnetic bits. At the same time, the data-processing speeds required by today's technology necessitate ultrafast switching in storage devices. Achieving both thermal stability and fast switching requires controlling the effective damping in magnetic nanoparticles. By carrying out a surface chemical analysis, we show that through exposure to ambient oxygen during processing, a nanomagnet can develop an antiferromagnetic sidewall oxide layer that has detrimental effects, which include a reduction in the thermal stability at room temperature and anomalously high magnetic damping at low temperatures. The in situ deposition of a thin Al metal layer, oxidized to completion in air, greatly reduces or eliminates these problems. This implies that the effective damping and the thermal stability of a nanomagnet can be tuned, leading to a variety of potential applications in spintronic devices such as spin-torque oscillators and patterned media.