Effect of Ge substitution on the magnetocaloric effect and exchange bias in Mn–Ni–Sn-Ge alloys: The role of Mn–Mn distance

Abstract

Abstract The effect of Ge substitution on the phase transitions, magnetocaloric effect, and exchange bias is studied in Mn50Ni40Sn10-xGex alloys by structural and magnetic analysis. Due to the lattice contraction induced by Ge substitution, the martensitic transformation temperature increases gradually, and the reentrant spin glass ground state is suppressed at x = 5 where zero-field-cooled exchange bias (ZEB) emerges. The maximum values of magnetic entropy change and ZEB are 19.2 J/kg·K for the field change of 5 T and 1.49 kOe at 10 K, which are achieved in Mn50Ni40Sn8Ge2 and Mn50Ni40Sn4Ge6, respectively. Importantly, the second-nearest Mn–Mn distance is found to be a key parameter affecting the magnetization change across the martensitic transformation and the ground state of these alloys. This work sheds new light on understanding the magnetism in Ni–Mn-based ferromagnetic shape memory alloys.