Large spin Hall magnetoresistance and its correlation to the spin-orbit torque in W/CoFeB/MgO structures

Abstract

The phenomena based on spin-orbit interaction in heavy metal/ferromagnet/oxide structures have been investigated extensively due to their applicability to the manipulation of the magnetization direction via the in-plane current. This implies the existence of an inverse effect, in which the conductivity in such structures should depend on the magnetization orientation. In this work, we report a systematic study of the magnetoresistance (MR) of W/CoFeB/MgO structures and its correlation with the current-induced torque to the magnetization. We observe that the MR is independent of the angle between the magnetization and current direction but is determined by the relative magnetization orientation with respect to the spin direction accumulated by the spin Hall effect, for which the symmetry is identical to that of so-called the spin Hall magnetoresistance. The MR of ~1% in W/CoFeB/MgO samples is considerably larger than those in other structures of Ta/CoFeB/MgO or Pt/Co/AlOx, which indicates a larger spin Hall angle of W. Moreover, the similar W thickness dependence of the MR and the current-induced magnetization switching efficiency demonstrates that MR in a non-magnet/ferromagnet structure can be utilized to understand other closely correlated spin-orbit coupling effects such as the inverse spin Hall effect or the spin-orbit spin transfer torques.

Origin of enhanced anomalous Hall effect in ultrathin Pt/permalloy bilayers

“…For instance, in W/CoFeB/MgO thin films, enhanced SMR can be induced by thin W layer, which is ascribed to the spin-orbit torque. 23 We believe it would not be accidental because AHE and SHE have the same physical nature in principle. Perhaps SMR model reveals more detailed mesoscopic mechanism to explain how the spin-dependent scattering is enhanced.…”

Dynamic coupling of ferromagnets via spin Hall magnetoresistance

“…Recently, physical phenomena, such as the spin torque [18][19][20][21][22][23][24][25] and magnetoresistance effects [26][27][28][29][30][31][32][33][34] , due to the spin Hall effect [35][36][37] in bilayers consisting of an insulating or metallic ferromagnet and a nonmagnetic heavy metal have attracted much attention. The latter, known as the spin Hall magnetoresistance, originates from the charge-spin conversion of an external electric current by the direct and inverse spin Hall effects, and has been observed by measuring the longitudinal and transverse electric currents, which are given by…”

Magnetoresistance generated from charge-spin conversion by anomalous Hall effect in metallic ferromagnetic/nonmagnetic bilayers

“…The key idea of the spin Hall magnetoresistance was the charge-spin conversion [10][11][12][13][14][15][16][17] caused by the spin Hall effect [18][19][20] originating from the spin-orbit interaction in nonmagnetic heavy metals. The spin Hall magnetoresistance was observed also in a metallic ferromagnetic/nonmagnetic bilayer [21][22][23][24].…”

“…These figures indicate that the magnetoresistance effect on the same order of the spin Hall magnetoresistance can be expected due to the charge-spin conversion caused by the anomalous Hall effect. It was recently shown that the anisotropic magnetoresistance and the planar Hall effect in the W/CoFeB/MgO heterostructure is one order of magnitude smaller than the spin Hall magnetoresistance [23]. Therefore, the magnetoresistance effect studied in the present work is considered to be measurable, although it has the same angular dependence with the planar Hall effect.…”