Enhanced Spin Current in Ni₈₁Fe₁₉/Cu–CuO_x Bilayer with Top and Sideways Oxidization

Abstract

Generation and manipulation of spin current are the cores of spintronic devices, which are intensely pursued. Heavy metals with strong spin–orbit coupling are commonly used for the generation of spin current, but are incompatible with the mass production of devices, and the polarization of spin current is limited to be in‐plane. Here, it is shown that the spin current with strong out‐of‐plane polarization component can be generated and transmitted in Ni81Fe19/Cu–CuOx bilayer with sideways and top oxidizations. The charge‐to‐spin current conversion efficiency can be enhanced through the spin currents consisting of both out‐of‐plane polarization (σz) and in‐plane polarization (σy) induced by spin‐vorticity coupling. Such a spin current is demonstrated to be closely related to the lateral oxidization gradient and can be controlled by changing the temperatures and times of annealing. The finding here provides a novel degree of freedom to produce and control the spin current in spintronic devices.

Electrical Manipulation of Orbital Current Via Oxygen Migration in Ni81Fe19/CuOx/TaN Heterostructure

“…Multiple peak fittings for the Cu 2p core-level spectra are performed on the basis of CuO (934.4 eV) and Cu/Cu 2 O (933.5 eV) peaks. [20] The relative Cu-O content in the CuO x layer can be estimated by the ratio of the peak area 𝜖 = S CuO /(S Cu/Cu2O +S CuO ), where S CuO and S Cu/Cu2O are the total areas of CuO and Cu/Cu 2 O peaks, respectively. The value of 𝜖 at different depths is extracted from the Cu valence evolution by multiple peak fittings for the Cu 2p core-level spectra.…”

“…[19] The nonreciprocal spin/orbital current with out-of-plane polarization can be generated in the Cu-CuO x layer by introducing top and sideway oxidizations. [20] Various mechanisms have been proposed to explain the origin of these exotic phenomena, such as orbital Hall effect (OHE), [14][15][16][17] interfacial Rashba effect [21][22][23][24] and spinvorticity coupling (SVC). [20,25] Numerous efforts have been exerted to manipulate the chargeto-spin/orbital current conversion efficiency and the SOT generation efficiency by changing the concentration of oxygen ions in oxidized light metal layers.…”

“…[20] Various mechanisms have been proposed to explain the origin of these exotic phenomena, such as orbital Hall effect (OHE), [14][15][16][17] interfacial Rashba effect [21][22][23][24] and spinvorticity coupling (SVC). [20,25] Numerous efforts have been exerted to manipulate the chargeto-spin/orbital current conversion efficiency and the SOT generation efficiency by changing the concentration of oxygen ions in oxidized light metal layers. [26][27][28] However, such a strategy is usually not feasible once the thin films or devices are fabricated, and the manipulation becomes irreversible.…”

Current-Induced Magnetization Switching in Light-Metal-Oxide/Ferromagnetic-Metal Bilayers via Orbital Rashba Effect

“…43−45 Given the insulating property of CuO x , the Oersted field as well as the spin−vortex coupling effect caused by the inhomogeneous spatial distribution of the drift velocity of the conduction electrons in CuO x are further ruled out. 46,47 To determine the torque generation efficiency for in-plane magnetized CoFeB/CuO x , two components of the torque effective field, i.e., damping-like (B DL ) and field-like (B FL ), are evaluated using transverse second-harmonic Hall measurements. Figure 3a shows the in-plane angular dependence of R xy…”

“…For comparison, we could not observe any magnetization reversal in CoFeB(2)/MgO(2) bilayers. Therefore, potential reversal mechanisms from CoFeB itself can be ruled out. − Given the insulating property of CuO x , the Oersted field as well as the spin–vortex coupling effect caused by the inhomogeneous spatial distribution of the drift velocity of the conduction electrons in CuO x are further ruled out. , …”