Enhanced unidirectional spin Hall magnetoresistance in a Pt/Co system with a Cu interlayer

Spin-dependent scattering at the nonmagnet/ferromagnet interface plays a key role in determining the amplitude of unidirectional spin Hall magnetoresistance (USMR), similar to giant magnetoresistance (GMR). We report the enhancement of USMR by inserting a thin Cu interlayer into the Pt/Co interface, where the Cu/Co system is well known to exhibit a large GMR. A measurement of the spin-orbit torque shows that the spin current injection into the Co layer is not modulated by the Cu interlayer. In addition, USMR increases with the Cu thickness for the ultrathin regime as the Cu/Co interface is formed, reaching a peak before decreasing, owing to the shunting effect. Our results suggest an interfacial origin of the enhanced USMR and highlight the close similarities between USMR and GMR.

Figure 1

(a) The layer structure of Pt/Cu(Au)/Co systems. (b) Schematic illustration of measurement geometry. $\phi$ is the azimuthal angle of the external magnetic field.

Figure 2

(a) Angle dependence of normalized first harmonic resistance. (b) Angle dependence of normalized second harmonic resistance at current density of ${1\times 10}^{11}\mathrm{A}/{\mathrm{m}}^2$, where the thermoelectric contribution is subtracted. (c) Normalized USMR as a function of current density. The solid lines in (a)–(c) show the fits to the data.

Figure 3

(a) The DL and (b) FL SOT efficiencies for the same samples shown in Figs. 2–2. Error bars are estimated from the fitting of second harmonic Hall resistance as a function of external magnetic field (see Supplemental Material [22]).

Figure 4

(a) Normalized USMR and (b) longitudinal resistance as a function of Cu(Au) thickness together with fitting curves. The inset in (a) is the Cu(Au) thickness dependence of $\mathrm{\Delta }{R}_{\mathrm{i}}/R_{\mathrm{i}}^2$ determined from the fitting and Eq. (3).