Magnetostriction and magnetic structure in annealed recrystallization of strain-forged ferromagnetic shape memory Fe–Pd–Rh alloys

Bulk ferromagnetic shape memory [formula omitted] and [formula omitted] (at. %) alloys were strain-forged to produce a 35%–40% reduction in thickness. The reduced alloys were thermally annealed at [formula omitted] for various times to induce recrystallization. The magnetostriction test demonstrated that the grain size reduction of recrystallization had a direct influence on the magnetic properties of the materials. The magnetostrictive strain measurements revealed that the strain-forged metal treated with thermal recrystallization to induce the fine-grained structure had a higher magnetostriction as well as a higher magnetostrictive susceptibility [formula omitted]. It was also found that at room temperature, the saturation magnetostriction [formula omitted] of the fine-grained Fe–Pd–Rh alloys strain-forged with thermal recrystallization was higher than that of those without grain size reduction [formula omitted], where [formula omitted] is [formula omitted]. In addition, with the magnetic field applied perpendicular to the sample's longitude, the fine-grained Fe–Pd–Rh material contracted by as much as [formula omitted]. This value is about three times higher than that of alloys without grain size reduction. Microstructure investigation indicated that a magnetic applied field normal to the sample's longitude caused high contraction [formula omitted] of the fine-grained Fe–Pd–Rh alloys, which could be ascribed mainly to the grain refinement as well as deformation twins or microtwins (transformation and transverse twins). The study demonstrates that the magnetostrictive strains of Fe–Pd–Rh alloys induced in the [formula omitted] martensite by the magnetic field can be attributed to the reorientation of the [formula omitted] martensite twin structures.