Fe and Co selective substitution in Ni₂MnGa: Effect of magnetism on relative phase stability

Abstract

We studied the effect of selective substitution in Fe and Co 3d elements on the structural and magnetic phase transitions in the prototypical magnetic shape memory alloy Ni–Mn–Ga. We determined the phase diagram for each elemental doping substitution by means of calorimetry and ac susceptibility measurements. An effort was made to substitute each constituent element by the same amounts of doping and to study the role of parameters other than electronic concentration in controlling phase stability. Specifically, selective doping with atoms of similar atomic radii but different magnetic properties allowed us to investigate the role of magnetic interactions on the relative phase stability of the ternary compound. We determined the entropy change associated with the martensitic transition for each quaternary alloy to obtain further information on the effect of magnetism on the relative stability of the involved phases exhibited by these compounds.

Keywords:

• magnetic shape memory alloys
• Ni₂MnGa
• phase transitions
• phase diagrams

Acknowledgements

This work received financial support from the CICyT (Spain), Project No. MAT2007–61200, and from CONACYT (44786-SEP-CONACYT 2003). X.M. acknowledges support from Comissionat per a Universitats i Recerca (CUR) del Departament d'Innovació, Universitats i Empresa de la Generalitat de Catalunya.