Quasi-Maser Operation Using Magnetic Tunnel Junctions

Quasi-maser operations using magnetic tunnel junctions (MTJs) that amplified the transmission of radio frequency (RF) signals through themselves are demonstrated. We measured the transmittance of heat-driven MTJs using a vector network analyzer and observed that transmittance S-21 >1 at sub-GHz frequencies. Furthermore, we installed two of these MTJs in a feedback-loop circuit and investigated the RF signal in the circuit. The results showed that the auto-oscillation mode of the RF signal appeared without phase synchronization of each MTJ because of the amplification effect. Our results will help develop a mechanism for producing coherent microwave signals using multiple MTJs.