Magnetostriction enhancement in ferromagnetic strain glass by approaching the crossover of martensite

Abstract

Owing to its unique nanostructure with nanosized strain domains embedded in the austenite matrix, ferromagnetic strain glass has recently been found to yield low-field large magnetostriction, providing an important principle for designing magnetostrictive materials. Considering that magnetostriction maximizes in the vicinity of the strain glass transition temperature, Tg that is usually below room temperature; it has inspired the search for a feasible approach to further enhance room temperature magnetostriction from an application point of view. Here, we report that approaching the martensite crossover through applying proper stress during annealing can effectively enhance room temperature magnetostriction of a random polycrystalline Fe67.7Pd32.3 strain glass alloy with Tg of 133 K from 73 to 95 ppm by ∼30%. The comparative results reveal that annealing with higher stress, e.g., 15 MPa, will deteriorate magnetostriction performance due to stress-induced martensites. Further transmission electron microscopy study reveals that enhanced magnetostriction is due to slightly enlarged strain nanodomains because the proper bias stress provides an extra driving force toward the martensite and helps to overcome the kinetic limitation, which may be a universal approach to achieve large magnetostriction in ferromagnetic strain glass.