When a current is passed through a non-magnetic metal with strong spin-orbit coupling, an orthogonal spin current is generated. This spin current can be used to switch the magnetization of an adjacent ferromagnetic layer or drive its magnetization into continuous precession. The interface, which is not necessarily sharp, and the crystallographic structure of the nonmagnetic metal can both affect the strength of current-induced spin-orbit torques. Here, we investigate the effects of interface intermixing and film microstructure on spin-orbit torques in perpendicularly magnetized Ta/Co₄₀Fe₄₀B₂₀/MgO trilayers with different Ta layer thickness (5 nm, 10 nm, 15 nm), greater than the spin diffusion length. Effective spin-orbit torques are determined from harmonic Hall voltage measurements performed at temperatures ranging from 20 K to 300 K. We account for the temperature dependence of damping-like and field-like torques by including an additional contribution from the Ta/CoFeB interface in the spin diffusion model. Using this approach, the temperature variations of the spin Hall angle in the Ta underlayer and at the Ta/CoFeB interface are determined separately. Our results indicate an almost temperature-independent spin Hall angle of $${{\boldsymbol{\theta }}}_{{\boldsymbol{SH}}}^{{\boldsymbol{N}}}\approx -{\bf{0.2}}$$θ SH N ≈ − 0.2 in Ta and a strongly temperature-dependent $${{\boldsymbol{\theta }}}_{{\boldsymbol{SH}}}^{{\boldsymbol{N}}}$$θ SH N for the intermixed Ta/CoFeB interface.

Spin-orbit-torque- (SOT) induced magnetization switching in a $\mathrm{Co}$/$\mathrm{Pt}$/$\mathrm{Co}$ trilayer, with two $\mathrm{Co}$ layers exhibiting magnetization easy axes orthogonal to each other is investigated. A $\mathrm{Pt}$ layer is used as a source of spin-polarized current as it is characterized by relatively high spin-orbit coupling. The spin Hall angle of $\mathrm{Pt}$, $\theta =0.08$, is quantitatively determined using the spin-orbit-torque ferromagnetic resonance technique. In addition, $\mathrm{Pt}$ serves as a spacer between two $\mathrm{Co}$ layers and depending on its thickness, different interlayer-exchange-coupling (IEC) energy between ferromagnets is induced. Intermediate IEC energies, resulting in a top $\mathrm{Co}$ magnetization tilted from the perpendicular direction, allows for SOT-induced field-free switching of the top $\mathrm{Co}$ layer. The switching process is discussed in more detail, showing the potential of the system for neuromorphic applications.

The magnetization dynamics in $\mathrm{W}/{\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$, ${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}/\mathrm{Pt}$ and $\mathrm{W}/{\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}/\mathrm{Pt}$ multilayers are investigated using spin-orbit-torque ferromagnetic resonance (SOT FMR) technique. An analytical model based on magnetization dynamics due to SOT is used to fit the heavy-metal (HM) thickness dependence of the symmetric and antisymmetric components of the SOT FMR signal. The analysis results in a determination of the properties of the HM layers, such as the spin Hall angle and the spin diffusion length. Spin Hall angles of $-0.36$ and 0.09 are found in the $\mathrm{W}/{\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ and ${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}/\mathrm{Pt}$ bilayers, respectively, which add up in the case of a $\mathrm{W}/{\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}/\mathrm{Pt}$ trilayer. More importantly, we determine the effective interfacial spin-orbit fields at both the $\mathrm{W}/{\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ and ${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}/\mathrm{Pt}$ interfaces, which are shown to cancel the Oersted field for particular thicknesses of the heavy-metal layers, leading to pure spin-current-induced dynamics and indicating the possibility of more efficient magnetization switching.

We report on the temperature variation of spin-orbit torques in perpendicularly magnetized W/CoFeB bilayers. Harmonic Hall voltage measurements in perpendicularly magnetized CoFeB reveal increased longitudinal and transverse effective magnetic field components at low temperatures. The damping-like spin-orbit torque reaches an efficiency of 0.55 at 19 K. Scanning transmission electron microscopy and X-ray reflectivity measurements indicate that considerable interface mixing between W and CoFeB may be responsible for strong spin-orbit interactions.