Deviation of the magnetization change from the structural phase transition temperature in polycrystalline Ni–Mn–Sn in low magnetic fields

Magnetization and resistivity were measured as a function of temperature in polycrystalline Ni–Mn–Sn Heusler alloys with a magnetocrystalline first order phase transition. At external magnetic fields <0.2 T the magnetization change associated with the phase transition happened at a temperature up to ∼5 K lower than the true phase transition temperature measured by electrical resistivity or predicted by thermodynamic theory. We associate this anomaly with magnetic exchange coupling between austenite and martensite phases coexisting near the transition.