Spin transfer torque switching dynamics in CoFeB/MgO magnetic tunnel junctions

Abstract

We perform atomistic simulations of spin transfer torque switching dynamics in CoFeB/MgO/CoFeB magnetic tunnel junctions. We base our study on Slonczewski's model parametrized following the approach of Zhang, Levy, and Fert. We utilize excitation modes and the contour integral of the magnetization to perform a deeper analysis of the switching mechanism driven by spin transfer torque. Our results show a magnetization reversal driven by the combination of coherent and nonuniform excitation modes. These can be nonuniform and initiated by a coherent mode of the magnetization, or domain wall nucleated depending on the lateral size, temperature, and current density injected into the system. Larger current densities result in stronger excitation of nonuniform modes making the switching more easily subjected to thermal excitations and structural imperfections such as edge damage. Our findings agree with experimental works on spin transfer torque switching in similar CoFeB/MgO-based systems, and they suggest the presence of complex features in the magnetization dynamics. The analysis and the results presented here can help to gain a deeper understanding of spin transfer torque dynamics in nanoscale devices.

Magnetisation switching dynamics induced by combination of spin transfer torque and spin orbit torque

“…This differs slightly from the case of a macrospin-derived approach, as in Ref. 58 , where for large the reversal can exhibit strong excitations of the non-collinear modes at such dimensions. This can likely be ascribed to the missing in-plane spacial dependence and angular dependence in the latter approach, which can lead to an overestimation of the torque acting on the system.…”

“…Small diameters are characterised by longer incubation time, as observed in Ref. 58 , resulting in larger critical current densities. Thus, STT-induced precessional switching sets a limitation to size scaling in a low temperature regime.…”

“…As discussed in Ref. 58 , STT-induced magnetisation dynamics is characterised by a rotation of the in-plane component and by either coherent reversal or non-collinear reversal of the out-of-plane component. The former is always observed and is caused by the STT symmetry, the latter depends on the size and magnitude of .…”

“…The former is always observed and is caused by the STT symmetry, the latter depends on the size and magnitude of . The excitation modes, introduced in the Method section, show an overall dominant coherent character of the dynamics in these cases, with excitation of the vortex and antivortex modes 58 for strong and large diameters. It is worth mentioning that when STT is modelled via the spin accumulation, the reversal mechanism is coherent up to diameters of 20 nm.…”

Interplay of Voltage Control of Magnetic Anisotropy, Spin-Transfer Torque, and Heat in the Spin-Orbit-Torque Switching of Three-Terminal Magnetic Tunnel Junctions

“…Consequently, STT has a negligible impact on v c in the larger devices unless sufficiently long pulses are applied. These observations suggest that STT does not contribute effectively to domain nucleation, but may promote fast reversal in small devices where the magnetization dynamics is more coherent [76,77].…”