Twisted magnetization states and inhomogeneous resonance modes in a Fe/Gd ferrimagnetic multilayer

TL;DR

This study investigates the static and dynamic magnetic properties of a Fe/Gd ferrimagnetic multilayer across a wide temperature range, revealing twisted magnetization states and inhomogeneous resonance modes through experimental and theoretical analysis.

Contribution

It provides the first detailed experimental and theoretical analysis of twisted magnetization states and inhomogeneous resonance modes in Fe/Gd multilayers.

Findings

Detection of transition between field-aligned and canted magnetic states.

Observation of two spectral branches corresponding to different inhomogeneous resonance modes.

Construction of the magnetic phase diagram of the Fe/Gd superlattice.

Abstract

Static and dynamic magnetic properties of a ferrimagnetic [Fe(35A)/Gd(50A)]x12 superlattice were investigated in a wide 4-300 K temperature range using magneto-optical Kerr effect (MOKE) and ferromagnetic resonance (FMR) techniques. The multilayer structure was sputtered on a transparent glass substrate which made it possible to perform MOKE measurements on both Fe and Gd terminated sides of the superlattice. These experiments allowed us to detect a transition between field-aligned and canted magnetic states on both sides of the film and to distinguish between the bulk and surface twisted phases of the superlattice. As a result, the experimental H-T magnetic phase diagram of the system was obtained. FMR studies at frequencies 7-36 GHz demonstrated a complex evolution of absorption spectra as temperature decreased from room down to 4 K. Two spectral branches were detected in the sample. Theoretical simulations show that the observed spectral branches correspond to different types of inhomogeneous resonance modes in the multilayer with non-uniform magnetization precession inside Gd layers.