Ferromagnetic composite with stress-insensitive magnetic permeability: Compensation of stress-induced anisotropies

Single-phase ferromagnets show deterioration of magnetic permeability when operating under a prestress due to the stress-induced anisotropy, which is a serious restriction for soft magnets. However, technologically, it is highly desired that soft magnets can maintain stable permeability under high stress. Here we report that a ferromagnetic Fe-Ga composite exhibits nearly unchanged magnetic permeability and coercivity even when subjected to compressive prestress as high as 200 MPa. Such stress-insensitive magnetic properties stem from the compensation of stress-induced anisotropies between the two ferromagnetic components with opposite magnetostriction signs (lambda > 0 for the bcc phase and lambda < 0 for the fcc phase). The magnetomechanical measurements and phase field simulations revealed that the stress-induced domain switching pathways are competitive between the bcc and the fcc phases, ruling out the prestress influence on magnetization. The present finding may provide a general recipe for designing soft magnets with stable magnetic properties under high stress.