Magneto-mechanical evaluation for twinning plane movement driven by magnetic field in ferromagnetic shape memory alloys

Rearrangement of martensite variants under magnetic field has been investigated by using single crystals of three ferromagnetic shape memory alloys: a disordered Fe–31.2 at.% Pd alloy, an ordered (degree of order ∼0.8) Fe3Pt, and stoichiometric Ni2MnGa. Each alloy transforms from a cubic parent phase to a tetragonal or pseudotetragonal martensite phase whose tetragonality is about 0.94 at low temperatures. We evaluated the magnetic shear stress τmag acting across the twinning plane under magnetic field, by using magnetic anisotropy constant and twinning shear, and compared it with the shear stress required for the rearrangement τreq, which is obtained from tensile or compressive tests. As a result, we confirmed that τmag is larger than τreq when the rearrangement of variants occurs by magnetic field and vice versa regardless of temperature and field direction.