Spin Torque Oscillators with Highly Spin-Polarized Heusler Alloy

An intriguing spin torque device is the spin torque oscillator (STO). An important issue for STOs from the viewpoint of practical use is to enhance the rf output power (Pout). Since Pout is roughly proportional to the square of the magnetoresistance (MR) ratio, a ferromagnetic material showing a large MR effect is a candidate for high-performance STO. In this study, we have developed high-power all-metal STOs with a full Heusler Co2Fe0.4Mn0.6Si (CFMS) showing a large MR effect. The present STOs consist of current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) stacks of CFMS \textbar Ag \textbar CFMS. A pillar-shaped STO showed clear auto-oscillation. The large Pout of 23.7 nW was obtained owing to its out-of-plane magnetization precession. Simultaneously, the oscillation linewidth showed the minimum value of 10 MHz. On the other hand, a point-contact-type STO showed auto-oscillation even at zero external magnetic field, and the oscillation mode was drastically changed as the bias current was increased. The large Pout for both STOs indicates the CPP-GMR devices with CFMS layers are promising for high performance STO.