Magnetic interactions governing the inverse magnetocaloric effect in martensitic Ni-Mn-based shape-memory alloys

Abstract

Ni-Mn-X Heusler-type alloys (X: group IIIB-VB elements) undergo martensitic transformations, and many of them exhibit magnetic shape-memory and field-induced effects, one of the most predominant being the inverse magnetocaloric effect. To understand the cause of the inverse magnetocaloric effect, which involves a magnetic entropy increase with applied field, it is necessary to understand the nature of the magnetic coupling in the temperature vicinity of the martensitic transition. We present results on neutron polarization analysis experiments on Ni-Mn-based martensitic Heusler systems, with which we show that around Ms, the magnetic short-range correlations at temperatures T < Ms are antiferromagnetic. We discuss the relationship of the magnetic coupling and the inverse magnetocaloric effect. © Springer-Verlag Berlin Heidelberg 2012.