UCLA

Spin waves are collective excitations in magnetically ordered materials. Early spin-wave devices find applications in microwave technologies. In more recent years, spin waves have been widely considered as an information carrier in the field of magnonics for energy-efficient applications. Spin waves in insulators are free from Ohmic losses but still suffer from magnetic damping. When it comes to thin films, even the ferrimagnetic insulator, yttrium iron garnet (YIG), with extremely low magnetic damping is far from ideal for practical device applications. The spin-wave damping, however, can be compensated with spin-orbit torque (SOT) sourcing from a high spin-orbit coupling (SOC) material in adjacent to the magnetic material. We demonstrate spin-wave amplification at the edge of spin-wave passband with a topological insulator (TI) as the SOC material. We also show that by using alternating Pt and Ta bars as the SOC materials to generate a SOT wave and matching it in phase with the spin waves, the spin waves can be efficiently amplified at a specific wavelength in the main spin-wave passband. On the other hand, the realization of low dissipative spin superfluid transport in a non-local spin transport configuration has been proposed theoretically, with some recent experimental signatures demonstrated. We show our non-local experimental results based on ferrimagnetic insulator YIG and antiferromagnetic insulator bismuth ferrite (BFO). Electrical control of spin superfluid transport in a magnetic Josephson junction is proposed and investigated numerically for practical spin superfluid device applications.