Spin–orbit torque switching in a T-type magnetic configuration with current orthogonal to easy axes

Abstract

Different symmetry breaking ways determine various magnetization switching modes driven by spin–orbit torques (SOT). For instance, an applied or effective field parallel to applied current is indispensable to switch magnetization with perpendicular anisotropy by SOT. Besides of this mode, here we experimentally demonstrate a distinct field-free switching mode in a T-type magnetic system with structure of MgO/CoFeB/Ta/CoFeB/MgO where a perpendicular layer with tilted easy axis was coupled to an in-plane layer with a uniaxial easy axis. Current was applied orthogonal to both easy axes and thus also normal to an in-plane effective field experienced by the perpendicular layer. Dynamic calculation shows perpendicular layer could be switched at the same time as the in-plane layer is switched. These field-free switching modes realized in the same T-type magnetic system might expedite the birth of multi-state spin memories or spin logic devices which could be operated by all electric manners.

Electric-field control of field-free spin-orbit torque switching via laterally modulated Rashba effect in Pt/Co/AlOx structures

“…We point out that our device has a distinctive advantage that the deterministic SOT switching polarity is electrically controllable. This electrical controllability cannot be achieved with previously reported ones demonstrating z- SOT using a hybrid FM/ferroelectric structure 30 , a wedged structure 36 , a tilted magnetic anisotropy 40 , 41 , a chirally coupled nanomagnets 42 , a structural asymmetry 38 , 43 , and a low crystal symmetry material 44 , 45 . Moreover, this electrical controllability offers programmable logic operations by utilizing the reversible and non-volatile characteristics (Supplementary Note 2 ).…”

“…We now discuss the physical origin of the electric-field-induced z- SOT. The first possible cause is the lateral modulation of PMA through voltage-controlled magnetic anisotropy (VCMA) effect 36 , 40 , 41 . The asymmetric gate voltages give rise to a gradient of PMA along the y -direction of which sign depends on the sign of Δ V G , resulting in a field-free switching.…”

Electric-field control of field-free spin-orbit torque switching via laterally modulated Rashba effect in Pt/Co/AlOx structures

“…We point out that our device has a distinctive advantage that the deterministic SOT switching polarity is electrically controllable. This electrical controllability cannot be achieved with previously reported ones demonstrating z-SOT through inversion symmetry breaking either by employing a material of low crystal symmetry [41,42] or by introducing structural asymmetry [37][38][39][43][44][45]. Moreover, this electrical controllability offers programmable logic operations in spintronic login-in-memory devices as we will demonstrate below.…”

“…We now discuss the physical origin of the electric field-induced z-SOT. The first possible cause is the lateral modulation of PMA through voltage-controlled magnetic anisotropy (VCMA) effect [37,43,44]. The asymmetric gate voltages give rise to a gradient of PMA along the y-direction of which sign depends on the sign of DVG, resulting in a field-free switching.…”

Prospect of Spin-Orbitronic Devices and Their Applications

“…Although the exact mechanism remains unclear ( Akyol et al., 2015 ), a gradient of the PMA or the saturation magnetization was thought to be responsible for the deterministic SOT switching. In other cases, the easy axis of the PMA-FM was tilted away from the out-of-plane direction either by annealing the sample under an in-plane magnetic field ( Kong et al., 2019 ) or by epitaxially depositing the SrIrO 3 /SrRuO 3 bilayer with tilted magnetocrystalline anisotropy on a (001)-oriented SrTiO 3 substrate ( Liu et al., 2019c ). Among them, each engineering methodology warrants sufficient asymmetry in the PMA for the field-free SOT-induced magnetization switching.…”