Superparamagnetic and superspin glass behaviors in the martensitic state of Ni 43.5 Co 6.5 Mn 39 Sn 11 magnetic shape memory alloy

The magnetic state of the low-temperature martensite in a Ni 43.5 Co 6.5 Mn 39 Sn 11 magnetic shape memory alloy (MSMA) is disclosed. At temperatures ( T ) above a critical temperature T f , the magnetization versus field [ M ( H ) ] curves display a sigmoid shape, show no magnetic hysteresis, and can be well fitted according to the Langevin model, confirming that the martensite shows superparamagnetic behavior at T > T f . On the other hand, the observation of a memory effect during the stop-and-wait protocol and the analysis of dynamic magnetic properties probed by ac susceptibility measurements unequivocally corroborate the superspin glass behavior of interacting magnetic clusters at T < T f . The present study provides significant insights into the magnetism of martensite in MSMAs.