Extremely High Ferromagnetic Resonance Frequency Induced by Triclinic Lattice Distortion in Epitaxial FeCo/MgAl₂O₄ (001) Films

Abstract

Theoretically, tetragonal lattice distortion of FeCo epitaxial films can result in a very large in‐plane magnetic anisotropy field, leading to an extremely high ferromagnetic resonance (FMR) frequency. In this study, Fe75Co25 thin films were epitaxially grown on (001) MgAl2O4 single crystal substrates. A triclinic lattice distortion with a≠b≠c, instead of a tetragonal one, was found in the FeCo films. The cubic symmetry breaking leads to a deviation of easy axes from the 〈100〉 directions, forming a distribution of magnetic moments with a strong perpendicular magnetic anisotropy (PMA) along the out‐of‐plane [001] directions and a deviation of the in‐plane components from the ( [100] and [010]) directions. The effective field of the former is as high as 1.5‐2.5 T, enough to overcome the thin film shape anisotropy, while that of the latter stays at a low value around 0.05 T. The strain induced PMA gradually relaxes to in‐plane for thicker films with a strained sublayer remains. As a result, an extremely high out‐of‐plane FMR frequency over 40 GHz was achieved, accompanied with a lower in‐plane FMR frequency around 8 GHz. This study provides a possible approach to prepare self‐biased soft magnetic films with extremely high resonance frequency for applications in microwave integrated circuits.This article is protected by copyright. All rights reserved.