Investigation of stiffness and damping constant of spin waves in a soft magnet Co100−xBx alloy

Abstract

In ferromagnets, alloying provides tunability of magnetic, electrical, and mechanical properties; however, its effect on magnetization has mostly been studied in terms of static properties. In this study, we investigate the stiffness and damping of spin waves in a cobalt-boron (Co100−xBx) alloy using an optical pump-probe technique. Coherent spin waves in Co100−xBx were excited by an optical spin–orbit torque from Pt. The dynamics of the spin wave were monitored on a picosecond timescale using the magneto-optical Kerr effect. From the oscillation period and relaxation of the spin wave, the stiffness and damping of the spin waves were determined. As the boron concentration increases from 0% to 35%, the spin wave stiffness decreases from 4.3 to 1.0 meV nm2, and the damping constant of the spin wave increases from 0.02 to 0.11. Such a large change suggests that B alloying has a significant impact on the spin-wave properties.