Optical and extreme UV studies of spin dynamics in metallic and insulating ferrimagnets

Abstract

We present all-optical studies of spin dynamics in two classes of ferrimagnets. Both sets of experiments use table-top laser based pump-probe techniques to examine the ultrafast and longer timescale spin excitations. We use visible / near infra-red time-resolved magneto-optical Kerr effect (tr-MOKE) to follow the spin dynamics of a series of metallic (FeCo) 1−x Gd x thin films with varying Gd content. Magnetic compensation in the films occurs at a Gd concentration of ≈26% and the spin dynamics of the films exhibit a non-monotonic variation in effective magnetization.We also examine spin dynamics in an insulating NiFe 2 O 4 spinel using ultrafast techniques up at extreme ultraviolet energies, which permit element-specific investigations. The element and time-resolved delay scans reveal a non-trivial interaction between spin excitations on the different magnetic sub-lattices of the magnetic insulator.