We study the voltage control of perpendicular magnetic anisotropy in an ultrathin Fe layer sandwiched between the Cr buffer and MgO tunneling barrier layers. A high-interface magnetic anisotropy energy of $2.1\mathrm{mJ}/{\mathrm{m}}^2$ is achieved in the Cr/ultrathin $\mathrm{Fe}/\mathrm{MgO}$ structure. A large voltage-induced perpendicular magnetic anisotropy change is observed under the negative-bias voltage applications for the case of the Fe layer thinner than 0.6 nm. The amplitude of the voltage-induced anisotropy energy change exhibits a strong Fe-thickness dependence and it reaches as high as $290\mathrm{fJ}/\mathrm{Vm}$. The observed high values of the surface anisotropy and voltage-induced anisotropy energy change demonstrate the feasibility of voltage-driven spintronic devices.

We study the dependence of the perpendicular magnetic anisotropy on the underlayer material in magnetic tunnel junction. Using several different 4d and 5d metals we identify an optimal seed layer in terms of high anisotropy, low mixing, and high thermal stability. In such systems we investigate the tunability of the anisotropy by means of electric fields. Especially, by using W as the underlayer of the CoFeB/MgO/CoFeB trilayer we could obtain good thermal stability that allows for annealing in the temperatures up to $450{}^{\circ }\mathrm{C}$, which results in high perpendicular anisotropy.

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.

Electrical transport in noncentrosymmetric materials departs from the well-established phenomenological Ohm’s law. Instead of a linear relation between current and electric field, a nonlinear conductivity emerges along specific crystallographic directions. This nonlinear transport is fundamentally related to the lack of spatial inversion symmetry. However, the experimental implications of an inversion symmetry operation on the nonlinear conductivity remain to be explored. Here, we report on a large, nonlinear conductivity in chiral tellurium. By measuring samples with opposite handedness, we demonstrate that the nonlinear transport is odd under spatial inversion. Furthermore, by applying an electrostatic gate, we modulate the nonlinear output by a factor of 300, reaching the highest reported value excluding engineered heterostructures. Our results establish chiral tellurium as an ideal compound not just to study the fundamental interplay between crystal structure, symmetry operations and nonlinear transport; but also to develop wireless rectifiers and energy-harvesting chiral devices.

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.