Ferromagnetic resonance linewidth in coupled layers with easy-plane and perpendicular magnetic anisotropies

TL;DR

This paper studies the ferromagnetic resonance linewidth in coupled magnetic bilayers with different anisotropies, revealing how interlayer exchange coupling influences linewidth behavior under varying magnetic fields.

Contribution

It introduces a macrospin model to explain the FMR linewidth behavior in coupled layers with easy-plane and perpendicular anisotropies, highlighting the effects of exchange coupling.

Findings

Elevated FMR linewidths occur below a characteristic field in antiferromagnetically coupled layers.

Linewidth increases monotonically in uncoupled and ferromagnetically coupled layers.

The macrospin model explains the linewidth behavior based on exchange interactions.

Abstract

Magnetic bilayers with different magnetic anisotropy directions are interesting for spintronic appli- cations as they offer the possibility to engineer tilted remnant magnetization states. We investigate the ferromagnetic resonance (FMR) linewidth of modes associated with two interlayer exchange- coupled ferromagnetic layers, the first a CoNi multilayer with a perpendicular magnetic anisotropy, and the second a CoFeB layer with an easy-plane anisotropy. For antiferromagnetic interlayer ex- change coupling, elevated FMR linewidths are observed below a characteristic field. This is in contrast to what is found in uncoupled, ferromagnetically coupled and single ferromagnetic layers in which the FMR linewidth increases monotonically with field. We show that the characteristic field at which there is a dramatic increase in FMR linewidth can be understood using a macrospin model with Heisenberg-type exchange coupling between the layers.