Interfacial spin-orbit torque without bulk spin-orbit coupling

Abstract

An electric current in the presence of spin-orbit coupling can generate a spin accumulation that exerts torques on a nearby magnetization. We demonstrate that, even in the absence of materials with strong bulk spin-orbit coupling, a torque can arise solely due to interfacial spin-orbit coupling, namely Rashba-Eldestein effects at metal/insulator interfaces. In magnetically soft NiFe sandwiched between a weak spin-orbit metal (Ti) and insulator (Al2O3), this torque appears as an effective field, which is significantly larger than the Oersted field and sensitive to insertion of an additional layer between NiFe and Al2O3. Our findings point to new routes for tuning spin-orbit torques by engineering interfacial electric dipoles.

Spin transport at interfaces with spin-orbit coupling: Phenomenology

“…To understand this contribution, note that carriers at the interface develop a net spin accumulation due to a phenomenon known as the Rashba-Edelstein effect [24][25][26][27][28]. If this spin accumulation is misaligned with the magnetization at the interface, it exerts a torque on the magnetization via the exchange interaction [1,2,[7][8][9][10]. In this geometry, the spin accumulation points along the −x×ẑ direction; thus the resulting torque on the magnetization points alonĝ m × (−x ×ẑ).…”

“…In heavy metal/ferromagnet bilayers, charge currents flowing parallel to the interface can manipulate the magnetization of the ferromagnetic layer [1][2][3][4][5][6][7]. The various mechanisms that drive this process require spin-orbit coupling [8][9][10][11], which couples the spin and orbital moments of carriers.…”

Theory of current-induced spin polarization in an electron gas

“…In semiconducting structures the reciprocal ISGE/EE is measured via optical detection of the current-induced spin polarization [20][21][22][23][24][25]. The ISGE/EE is also measured by analyzing the torques exercised, via exchange coupling, by the non-equilibrium polarization on the magnetization of an adjacent ferromagnetic system [26][27][28][29][30][31][32]. Recently this has been extended also to antiferromagnets [33].…”

Temperature dependence of spin-orbit torques across the magnetic compensation point in a ferrimagnetic TbCo alloy film

“…DOI: 10.1103/PhysRevB.96.064410 In the last five years, ferromagnetic films in contact with heavy metals with strong spin-orbit coupling have attracted interest for their potential utility in nonvolatile random access memory elements. In these systems, current-induced spin-orbit torques (SOTs) [1,2] on the magnetization can be induced by the Rashba-Edelstein effect at the interface [3,4] and by spin currents injected from the heavy metal due to the spin Hall effect [2,. SOTs with both a fieldlike and dampinglike character can manifest in such systems, with the latter capable of driving magnetization switching [1][2][3][4][5]7,9,[11][12][13]15,21,22,24] and magnetic domain wall motion [26][27][28][29][30][31].…”

“…In these systems, current-induced spin-orbit torques (SOTs) [1,2] on the magnetization can be induced by the Rashba-Edelstein effect at the interface [3,4] and by spin currents injected from the heavy metal due to the spin Hall effect [2,. SOTs with both a fieldlike and dampinglike character can manifest in such systems, with the latter capable of driving magnetization switching [1][2][3][4][5]7,9,[11][12][13]15,21,22,24] and magnetic domain wall motion [26][27][28][29][30][31]. SOTs have been identified and quantified by a variety of techniques including spin-torque ferromagnetic resonance [2,7,14,17,19,25], quasistatic magnetization tilting probed through harmonic voltage measurements [6,[8][9][10][11][12][13]17,[19][20][21][22][23][24][25]…”