Impact of in-plane currents on magnetoresistance properties of an exchange-biased spin valve with an insulating antiferromagnetic layer

The impact of in-plane alternating currents on the exchange bias, resistance, and magnetoresistance of a Co₈₅Fe₁₅∕Ni0.85Co0.15O∕Co₈₅Fe₁₅∕Cu∕Co₈₅Fe₁₅ spin valve is studied. With increasing current, the resistance is increased while the maximum magnetoresistance ratio decreases. Noticeably, the reversal field of the pinned layer is systematically suppressed in both field sweeping directions. Since Ni0.85Co0.15O is a good insulator, it is expected that the ac flows only in the Co₈₅Fe₁₅∕Cu∕Co₈₅Fe₁₅ top layers, thus ruling out any presence of spin-transfer torque acting on the spins in the antiferromagnetic layer. Instead, our measurements show clear evidence of the influence of Joule heating caused by the current. Moreover, results from temperature-dependent measurements very much resemble those of the current dependence, which indicates that the effect of Joule heating plays a major role in the current-in-plane spin-valve configurations. The results also suggest that spin-transfer torques between ferromagnetic layers might still exist and compete with the exchange bias at sufficiently high currents.