Exchange bias caused by field-induced spin reconfiguration in Ni-Mn-Sn

Abstract

Exchange bias is observed in ferromagnetic/antiferromagnetic (FM/AF) layered stacks and in materials with neighboring ferromagnetic and antiferromagnetic granules. The latter is commonly observed in Ni-Mn-based martensitic Heusler alloys. In general, the exchange-bias effect is identified as horizontally shifted hysteresis loop when the system is field cooled from high temperatures. We report here loop shifts not only under field-cooled but also under zero-field-cooled conditions in magnetically granular martensitic ${\mathrm{Ni}}_{50}{\mathrm{Mn}}_{50\ensuremath{-}x}{\mathrm{Sn}}_{x}$ Heusler alloys in the compositional range $13.0\ensuremath{\ge}x\ensuremath{\ge}8.9$. Under zero-field-cooled conditions, the initially applied field can carry the system over energy barriers and stabilize a spin-reconfigured state so that a negatively shifted hysteresis loop can also occur here as in the field-cooled state. Spin reconfiguration occurs when the relative size of the AF and FM regions as well as the relative strength of the of AF and FM interactions are in balance.