Spin Wave Frequency Variations Due to the Spin Glass Behavior in Co/CoPt Magnetic Multilayers

Abstract

In this paper, the spin wave frequency for a Co/CoPt multilayer is calculated. It is suggested that there is a low spin deviation from the equilibrium state, so a linearized Landau–Lifshitz equation is used. Using the mean field theory approach, we calculated the effect of a random crystal field on each magnetic layer which is related to the random interacting spins at the interface of two layers. When the interface of two magnetic layers is not smooth, random interactions become dominant at the interface of exchange-biased nanoparticles. Due to the defects presented at the interface of the Co/CoPt multilayer, we suggested that the interface performs like a spin glass system. In a mentioned situation, spin-glass-like spins at the interface reduce the strength of exchange coupling between the two layers and an applied external field polarizes the spins at the interface. With an increasing applied magnetic field, the spin glass regions are destroyed and interface spins align with the direction of the external field which change the strength of exchange coupling. So the strength of coupling between the two layers is dependent on the external field. For stronger external fields, random effects due to the spin glass behavior disappear. We also calculated the difference between frequencies of Stokes and anti-Stokes spin waves and their intensity ratio. Results are in good agreement with experimental data.