Spin-orbit field switching of magnetization in ferromagnetic films with perpendicular anisotropy

Abstract

As an alternative to conventional magnetic field, the effective spin-orbit field in transition metals, derived from the Rashba field experienced by itinerant electrons confined in a spatial inversion asymmetric plane through the s-d exchange interaction, is proposed for the manipulation of magnetization. Magnetization switching in ferromagnetic thin films with perpendicular magnetocrystalline anisotropy can be achieved by current induced spin-orbit field, with small in-plane applied magnetic field. Spin-orbit field induced by current pulses as short as 10 ps can initiate ultrafast magnetization switching effectively, with experimentally achievable current densities. The whole switching process completes in about 100 ps.Ultrafast manipulation of magnetization is currently under intense investigation, partly driven by the ever increasing demand in information industry, partly inspired by the intriguing physics involved. Traditional methods use pulsed magnetic field to realize ultrafast switching of magnetization, through the spiral motion of magnetization in a magnetic field, applied in the inverse direction of the magnetization. However, due to domain wall instability 1 , ultrashort field pulses bring about stochastic behavior, thus imposing limitations on the ultimate switching speed 2 . In practice, the limitation on this switching scheme is related to the difficulty in the generation of picosecond, strong magnetic field pulses, which entails the use of relativistic electron bunches nowadays. Precessional switching scheme, in which the magnetic field is applied perpendicular to the initial magnetization direction, circumvents this problem by maximizing the precession torque experienced by the magnetization 3 . The deficit of precessional switching is manifested by the needed precise control of the pulse duration, on the time scale of the magnetization's precession period. Instead of the conventional magnetic field, alternative means, such as light 4 , electric field 5 and electric current 6 , can be used to manipulate magnetization. Recently, the effective spin-orbit field acting on the magnetization attracts much attention because of its potential applications. This spin-orbit field in transition metals results from the Rashba field 7 experienced by itinerant electrons confined in a spatial inversion asymmetric potential through the s-d exchange interaction 8 . Reversible switching of magnetization in perpendicularly magnetized Co nanodots was already demonstrated 9 , making the speculation of employing the spin-orbit field to control magnetization in ferromagnetic metals more than mere imagination, although the underlying mechanism responsible for the observed switching is still elusive. It is proposed, as will be shown in the following by macrospin simulation, that the pure spin-orbit field, in combination a) Electronic mail: dwwang@nudt.edu.cn with the precessional motion induced by it, can explain qualitatively the observed experimental results . In addition, the feasibility of precessional switching utili...

Deterministic field-free switching of a perpendicularly magnetized ferromagnetic layer via the joint effects of the Dzyaloshinskii–Moriya interaction and damping- and field-like spin–orbit torques: an appraisal

“…Until now, the role of FLT in SOT switching is remain vague. Recent works have pointed out that the FLT can be much larger than SLT in some material combinations and it is possible to use FLT to switch the magnetization [23,24].…”

Magnonic momentum transfer force on domain walls confined in space

“…Besides GHz magnetic field, local injection of high density current [30] can also initiate magnetization oscillation through the STT effect. Elastic waves [31] and spin-orbit field [32] in properly engineered material systems can serve as alternative means to locally exciting SWs that subsequently propagate to activate DWM.…”

Coherent sub-nanosecond switching of perpendicular magnetization by the field-like spin-orbit torque without external magnetic field

“…Current-induced SOT is often explained in terms of the field-like and the Slonczewski torques [1,7,23]. Recent experimental studies [24][25][26][27][28] found that the fieldlike torque can be much larger than the Slonczewski torque in some material combinations, and this field-like torque is also capable of switching the magnetization [29]. Here, we investigate the potential of SOT switching in the case where the field-like torque is predominant and combined with the Slonczewski torque.…”