Control of Critical Current of Intrinsic Josephson Junctions Due to Spin Injection

We have investigated the influence of the ferromagnet magnetization on the critical current I_c of the intrinsic Josephson junctions (IJJs) in Co/Au/Bi₂Sr₂CaCu₂O_y(BSCCO) mesa structures under applied magnetic fields parallel to the layer. The mesa structure with lateral dimensions of 5×5 μm² and 2×13 μm² were fabricated by using electron beam lithography, photolithography and Ar ion milling. Before an application of magnetic field B, the current-voltage characteristics of the mesa showed the typical multiple resistive branches with hysteresis similar to those of conventional IJJs. However, by applying B the I_c was considerably suppressed and the I_c-B curve showed hysteresis in contrast to conventional IJJs. Furthermore, the suppression of I_c was found to be minimized at the coercive filed of the Co layer. This implies that the I_c is significantly affected by the domain structure of the Co formed on IJJs. From these results we found that the I_c of IJJs in the Co/Au/BSCCO mesa can be control by small magnetic field and the hybrid structure of ferromagnet and IJJs might be applicable for a switching device and other spintronics devices.