Optical spin pumping and magnetization switching in ferromagnets

Abstract

Motivated by recent experiments on all-optical magnetization switching (AOS), we analyze theoretically optical spin pumping in ferromagnetic metals. It is shown that spin polarizations, induced by linearly and circularly polarized pump pulses, can be comparable in magnitude. We assume that the photoinduced spin polarization influences ultrafast light-induced magnetization dynamics in ferromagnets. In particular, it plays a crucial role in AOS. We analyze the light-induced magnetization dynamics in a system of localized and itinerant spins coupled by s-d exchange interaction, assuming that light heats up the itinerant electrons and, in addition, changes their spin polarization. When the pumped spin polarization has an appropriate sign and magnitude, it triggers magnetization switching. We find that temporal evolution of the magnetization is determined by a complicated interplay between heating, the photoinduced spin polarization, and spin relaxation.