Complex magnetic behavior of the heusler alloy - Cu<inf>2</inf>Mn<inf>0.75</inf>Fe<inf>0.25</inf>Al

We investigated the structural and magnetic properties of Cu2Mn1-xFexAl (x =0.25 , 0.5, 0.75) alloys. Among the three compositions, only x =0.25 composition crystallizes in single phase with L 21 structure but its magnetic response indicates a complex magnetic structure. The magnetic isotherms were fitted to modified Langevin equation which indicates the presence of clusters with large magnetic moment. The ac susceptibility studies showed the presence of a superparamagnetic phase in the system over and above ferromagnetic order. To determine the nature of the interactions among the clusters, the variation of freezing temperature (Tf) with applied ac frequency was analyzed using different models (Néel-Arrhenius, Vogel-Fulcher, and critical slowing down model).