Dual-mode ferromagnetic resonance is observed in FeCoB/Ru/FeCoB trilayer synthetic antiferromagnets with uniaxial in-plane magnetic anisotropy. The optical mode is present in the (0–108 Oe) magnetic field range, where the top and bottom layer magnetizations are aligned in opposite directions. The strong acoustic mode appears, when the magnetic field exceeds the 300 Oe value, which corresponds to the flop transition in the trilayer. Magnetic field and angular dependences of resonant frequencies are studied for both optical (low-field) and acoustic (high field) modes. The low-field mode is found to be anisotropic but insensitive to the magnetic field value. In contrast, the high field mode is quasi-isotropic, but its resonant frequency is tunable by the value of the magnetic field. The coexistence of two modes of ferromagnetic resonance as well as switching between them with the increase in the magnetic field originates from the difference in the sign of interlayer coupling energy at the parallel and antiparallel configurations of the synthetic antiferromagnet. The dual-mode resonance in the studied trilayer structures provides greater flexibility in the design and functionalization of micro-inductors in monolithic microwave integrated circuits.

Heusler Co2FeSi films with a uniaxial magnetic anisotropy and high ferromagnetic resonance frequency f r were deposited by an oblique sputtering technique on Ru underlayers with various thicknesses t Ru from 0 nm to 5 nm. It is revealed that the Ru underlayers reduce the grain size of Co2FeSi, dramatically enhance the magnetic anisotropy field H K induced by the internal stress from 242 Oe (1 Oe = 79.5775 A⋅m−1) to 582 Oe with an increment ratio of 2.4, while a low damping coefficient remains. The result of damping implies that the continuous interface between Ru and Co2FeSi induces a large in-plane anisotropic field without introducing additional external damping. As a result, excellent high-frequency soft magnetic properties with f r up to 6.69 GHz are achieved.

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.