Interface-driven spin-torque ferromagnetic resonance by Rashba coupling at the interface between nonmagnetic materials

Abstract

The Rashba-Edelstein effect stems from the interaction between the electron's spin and its momentum induced by spin-orbit interaction at an interface or a surface. It was shown that the inverse Rashba-Edelstein effect can be used to convert a spin-into a charge current. Here, we demonstrate that a Bi/Ag Rashba interface can even drive an adjacent ferromagnet to resonance. We employ a spin-torque ferromagnetic resonance excitation/detection scheme which was developed originally for a bulk spin-orbital effect, the spin Hall effect. In our experiment, the direct Rashba-Edelstein effect generates an oscillating spin current from an alternating charge current driving the magnetization precession in a neighboring permalloy (Py, Ni80Fe20) layer. Electrical detection of the magnetization dynamics is achieved by a rectification mechanism of the time dependent multilayer resistance arising from the anisotropic magnetoresistance.Conventional spintronics relies on the exchange interaction between conduction electrons on one side and localized spins in magnetic materials on the other side [1]. Stimulated by the experimental demonstration of spinto charge current conversion using bulk spin Hall effects (SHE), these kind of spin-orbital phenomena were actively investigated in the last decade and opened up the door to the research field of spin-orbitronics [2][3][4][5]. SHEs can be investigated by means of spin-current injection from a ferromagnet (FM) into materials with large spinorbit coupling, usually normal metals (NM) such as Pt or Pd [6], and sensing the generated voltage generated by means of the inverse spin Hall effect (ISHE) [7][8][9][10][11][12][13][14]. Other interesting applications of SHEs are the effective magnetization switching of nanomagnets or the movement of domain walls [15][16][17]. Furthermore, the ferromagnetic linewidth modulation as well as the excitation of spin waves and ferromagnetic resonance by SHE was demonstrated in ferromagnetic metals and insulators [18][19][20][21][22]. The SHE is a bulk effect occurring within a certain volume of the NM determined by the spin-diffusion length. The conversion efficiency can be expressed by a materialspecific parameter, the spin Hall angle γ SHE [4].Very recently, it has been shown that the inverse Rashba-Edelstein effect (IREE) can also be used for transformation of a spin-into a charge current [23][24][25][26]. The IREE is the inverse process to the Rashba-Edelstein effect (REE) [27]. The REE originates from spin-orbit interaction in a 2D electron gas at interfaces or surfaces, which effectively produce a steady non-equilibrium spin polarization from a charge current driven by an electric field. The Hamiltonian of this interaction is given by [23]: H R = α R (k ×ê z ) · σ, where α R is the Rashba coefficient, e z is the unit vector in z-direction [see Fig. 1(b,c)] and σ is the vector of Pauli matrices. As a result of this interaction the dispersion curves of the 2D electron gas are spin-split if α R = 0, as illustrated in Fig. 1(a). Analogous to the spin Ha...

Interface-induced phenomena in magnetism

“…The inverse Edelstein effect, in which an incident spin current is converted to a charge current, was demonstrated experimentally for non-topological two-dimensional states at the Ag/Bi interface [Rojas-Sánchez et al ., 2013; Zhang et al ., 2015b]. For Ag/Bi interfaces it has also been demonstrated that spin transfer torques on a neighboring ferromagnetic layer are consistent with interfacial conversion [Jungfleisch et al ., 2016a]. …”

Giant Anisotropy of Gilbert Damping in Epitaxial CoFe Films

“…They were fabricated into 10 µm×40 µm bars by photolithography and ion milling. Coplanar waveguides with 100nm thick Au were subsequently fabricated [18,35]. For each layer structure, 14 devices with different orientations were fabricated, as shown in Fig.…”

Role of interface quality for the spin Hall magnetoresistance in nickel ferrite thin films with bulk-like magnetic properties

“…Last but not least, the bulk spin Hall effect is not the only cause for the conversion of a charge current into a pure spin current in a NM. It is quite possible that contributions from the spin-galvanic effect [26][27][28][29][30][31][32] arising at the NFO/NM interface also give rise to additional contributions to the SMR. As the spin-galvanic effect is caused by spin-orbit fields as a result of the broken inversion symmetry at the NFO/NM interface, it is quite possible that such a contribution depends on the charge current direction.…”