Spin Damping in Ultrathin Magnetic Films

Abstract

This chapter reviews the origin of the damping of spin motions in ultra-thin ferromagnetic films and multilayer structures, with focus on the linear response regime probed by ferromagnetic resonance or Brillouin light scattering. We begin with a description of the spin response provided by the Landau-Lifshitz equation, which ascribes damping to dissipative processes of intrinsic origin. It is noted that the form of the damping term should be modified in anisotropic materials, and explicit expressions are provided for the form of a generalized damping term in bulk matter. We then turn to an extrinsic damping mechanism, the two-magnon process, which, recent experiments illustrate, plays a major role in spin damping in ultrathin films and multilayer structures. The history of this mechanism in ferromagnetic resonance studies is reviewed, the physical reasons for it to be active in ultrathin ferromagnetic films are discussed, and we the review recent experimental studies that have verified central predictions of the theory.