Magnetic correlations in martensitic Ni-Mn-based Heusler shape-memory alloys: Neutron polarization analysis

In ferromagnetic Ni-Mn-based Heusler alloys undergoing martensitic transformations, a sudden drop in the magnetization is observed as the temperature decreases through the martensitic-transformation temperature Ms. To understand the cause of the drop and thereby the nature of the magnetic coupling in this temperature region, we carry out neutron-polarization-analysis experiments on two prototypes, Ni50 Mn40 Sb10 and Ni50 Mn37 Sn13. We show that in the vicinity of Ms, the magnetic correlations at temperatures T< Ms are antiferromagnetic, whereas they are ferromagnetic above Ms and well beyond the Curie temperature of the austenitic state.