Magnetic interactions in the martensitic phase of Mn rich Ni-Mn-In shape memory alloys

Abstract

The magnetic properties of Mn(2) Ni (1+ x )In(1- x ) (x = 0.5, 0.6, 0.7) and Mn(2- y) Ni (1.6+ y)In(0.4) (y = -0.08, -0.04, 0.04, 0.08) shape memory alloys have been studied. Magnetic interactions in the martensitic phase of these alloys are found to be quite similar to those in Ni(2)Mn(1+ x)In(1- x) type alloys. Doping of Ni for In not only induces martensitic instability in Mn(2)NiIn type alloys but also affects magnetic properties due to a site occupancy disorder. Excess Ni preferentially occupies X sites forcing Mn to the Z sites of X(2)YZ Heusler composition resulting in a transition from ferromagnetic ground state to a state dominated by ferromagnetic Mn(Y)-Mn(Y) and antiferromagnetic Mn(Y)-Mn(Z) interactions. These changes in magnetic ground state manifest themselves in observation of exchange bias effect even in zero field cooled condition and virgin magnetization curve lying outside the hysteresis loop.