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Register a new userRashba-Edelstein Magnetoresistance in Metallic Heterostructure
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We report the observation of magnetoresistance originating from Rashba spin-orbit coupling (SOC) in a metallic heterostructure: the Rashba-Edelstein (RE) magnetoresistance. We show that the simultaneous action of the direct and inverse RE effects in a Bi/Ag/CoFeB trilayer couples current-induced spin accumulation to the electric resistance. The electric resistance changes with the magnetic-field angle, reminiscent of the spin Hall magnetoresistance, despite the fact that bulk SOC is not responsible for the magnetoresistance. We further found that, even when the magnetization is saturated, the resistance increases with increasing the magnetic-field strength, which is attributed to the Hanle magnetoresistance in this system.
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We report the observation of magnetoresistance (MR) originating from the orbital angular momentum transport (OAM) in a Permalloy (Py) / oxidized Cu (Cu*) heterostructure: the orbital Rashba-Edelstein magnetoresistance. The angular dependence of the MR depends on the relative angle between the induced OAM and the magnetization in a similar fashion as the spin Hall magnetoresistance (SMR). Despite the absence of elements with large spin-orbit coupling, we find a sizable MR ratio, which is in contrast to the conventional SMR which requires heavy elements. By varying the thickness of the Cu* layer, we confirm that the interface is responsible for the MR, suggesting that the orbital Rashba-Edelstein effect is responsible for the generation of the OAM. Through Py thickness-dependence studies, we find that the effective values for the spin diffusion and spin dephasing lengths of Py are significantly larger than the values measured in Py / Pt bilayers, approximately by the factor of 2 and 4, respectively. This implies that another mechanism beyond the conventional spin-based scenario is responsible for the MR observed in Py / Cu* structures originated in a sizeable transport of OAM. Our findings not only unambiguously demonstrate the current-induced torque without using any heavy element via the OAM channel but also provide an important clue towards the microscopic understanding of the role that OAM transport can play for magnetization dynamics.
Thanks to its unique symmetry, the unidirectional spin Hall and Rashba-Edelstein magnetoresistance (USRMR) is of great fundamental and practical interest, particularly in the context of reading magnetization states in two-terminal spin-orbit torque switching memory and logic devices. Recent studies show that topological insulators could improve USRMR amplitude. However, the topological insulator device configurations studied so far in this context, namely ferromagnetic metal/topological insulator bilayers and magnetically doped topological insulators, suffer from current shunting by the metallic layer and low Curie temperature, respectively. Here, we report large USRMR in a new material category - magnetic insulator/topological insulator bi-layered heterostructures. Such structures exhibit USRMR that is about an order of magnitude larger than the highest values reported so far in all-metal Ta/Co bilayers. We also demonstrate current-induced magnetization switching aided by an Oersted field, and electrical read out by the USRMR, as a prototype memory device.
It is well known that a current driven through a two-dimensional electron gas with Rashba spin-orbit coupling induces a spin polarization in the perpendicular direction (Edelstein effect). This phenomenon has been extensively studied in the linear response regime, i.e., when the average drift velocity of the electrons is a small fraction of the Fermi velocity. Here we investigate the phenomenon in the nonlinear regime, meaning that the average drift velocity is comparable to, or exceeds the Fermi velocity. This regime is realized when the electric field is very large, or when electron-impurity scattering is very weak. The quantum kinetic equation for the density matrix of noninteracting electrons is exactly and analytically solvable, reducing to a problem of spin dynamics for unpaired electrons near the Fermi surface. The crucial parameter is $gamma=eEL_s/E_F$, where $E$ is the electric field, $e$ is the absolute value of the electron charge, $E_F$ is the Fermi energy, and $L_s = hbar/(2malpha)$ is the spin-precession length in the Rashba spin-orbit field with coupling strength $alpha$. If $gammall1$ the evolution of the spin is adiabatic, resulting in a spin polarization that grows monotonically in time and eventually saturates at the maximum value $n(alpha/v_F)$, where $n$ is the electron density and $v_F$ is the Fermi velocity. If $gamma gg 1$ the evolution of the spin becomes strongly non-adiabatic and the spin polarization is progressively reduced, and eventually suppressed for $gammato infty$. We also predict an inverse nonlinear Edelstein effect, in which an electric current is driven by a magnetic field that grows linearly in time. The conductivities for the direct and the inverse effect satisfy generalized Onsager reciprocity relations, which reduce to the standard ones in the linear response regime.
Rashba effect describes how electrons moving in an electric field experience a momentum dependent magnetic field that couples to the electron angular momentum (spin). This physical phenomenon permits the generation of spin polarization from charge current (Edelstein effect), which leads to the buildup of spin accumulation. Spin accumulation due to Rashba Edelstein effect has been recently reported to be uniform and oriented in plane, which has been suggested for applications as spin filter device and efficient driving force for magnetization switching. Here, we report the X-ray spectroscopy characterization Rashba interface formed between nonmagnetic metal (Cu, Ag) and oxide (Bi$_{2}$O$_{3}$) at grazing incidence angles. We further discuss the generation of spin accumulation by injection of electrical current at these Rashba interfaces, and its optical detection by time resolved magneto optical Kerr effect. We provide details of our characterization which can be extended to other Rashba type systems beyond those reported here.
We have studied spin-orbit (SO) field in Ni$_{80}$Fe$_{20}$(Py)/W/Pt trilayer by means of spin-torque ferromagnetic resonance, and demonstrated that the W/Pt interface generates an extra SO field acting on the Py layer. This unprecedented field originates from the following three processes, 1) spin accumulation at W/Pt interface via the Rashba-Edelstein effect, 2) diffusive spin transport in the W layer, and 3) spin absorption into the Py layer through accumulation at the Py/W interface. Our result means that we can create extra SO field away from the ferromagnet/ metal interface and control its strength by a combination of two different metals.
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