Eddy current suppression and soft magnetism enhancement in FeGaB-based magnetic composites with alumina lamination

Abstract

FeGaB thin films have excellent magnetostrictive and soft magnetic properties. Unfortunately, severe eddy current loss (ECL) due to its low resistivity makes its employment in energy-efficient structures challenging. Inserting insulating layers into magnetostrictive films is an effective technique to suppress ECL and enhance soft magnetic characteristics. Unresolved is how to exhaustively account for multiple contributing factors and obtain the optimal composite materials design. This study constructed an ECL simulation model of a soft magnetic composite (SMC) using finite element analysis in the COMSOL multiphysics software. To unify the two competing conditions of ECL suppression and magnetostriction reduction, the impacts of inserted alumina (thickness and the number of layers), FeGaB size (thickness and area), and applied frequency (0.01–1 GHz) were studied. SMC inserted with four layers of 5 nm Al2O3 can achieve remarkable overall performance, including good ECL suppression (85 %) but slightly reduced magnetostriction (1.8 %). Moreover, it was revealed that the ECL suppression has a size effect at high frequencies (1 GHz) when the SMC thickness surpasses 0.6–1 μm. To achieve the unification of simulation and experiment, a 120 nm/(Al2O3 5 nm/FeGaB 120 nm)4 SMC was produced and compared to a single-layer thin film of FeGaB. The SMC showed a superior soft magnetic characteristic and permeability after inserting Al2O3 sheets. Its ultra-low coercivity (0.017 Oe) resulted from the excellent material interface and the domain wall elimination; the permeability was enhanced by the frequency width half maximum lowered to 0.48 GHz, and the higher value of the imaginary component of magnetic permeability was 1303. Consequently, the experiment confirmed that the improvement in the dynamic response characteristics of the SMC is mainly attributable to the suppression of ECL and the enhancement of soft magnetic properties. The composite magnetic film in this study provides a potential solution for energy-efficient high-frequency structures.