LAUSR

Abstract We study compositional and thermal dependences of lattice parameters and twinning stress σ TW in Ni 50-x Mn 25-y Ga 25-z Co x Cu y + z magnetic shape memory alloys with non-modulated tetragonal crystal structure. The σ TW was found to decrease with increasing temperature with a slope from −0.0076 to −0.0181 MPa/K. The σ TW  = 0.47–0.81 MPa values measured near composition-specific austenite transformation temperatures T A were discovered to depend linearly on the c / a ratio with a slope of 14 MPa. We predict that the further decrease of c / a ratio to the level of 1.085–1.104 can result in extremely low σ TW  ≈ 0.1 MPa in non-modulated martensite.