A second-order ferromagnetic transition in the martensitic state of Ni49.5 Mn32.5 Cu4 Sn14: A critical behavior study

A second-order ferromagnetic transition is observed in the martensitic state of Ni49.5 Mn32.5 Cu4 Sn14 alloy and the critical behavior around the transition is investigated by dc magnetization measurements. With the help of modified Arrott plots, Kouvel-Fisher method, and Widom scaling relation, the values of TcM (ferromagnetic transition temperature in the martensite), and critical exponents: ? (associated with the spontaneous magnetization), ? (relevant to the initial susceptibility), and d (associated with the critical magnetization isotherm) are obtained. The scaling plots show that the obtained values of the critical exponents are reliable. The values of the critical exponents of Ni49.5 Mn32.5 Cu4 Sn14 are different from those predicted by several theoretical models, i.e., mean-field theory, three-dimensional Heisenberg model, and three-dimensional Ising model. The magnetic interactions exhibit two different behaviors: long-range magnetic interaction below TcM and local magnetic interaction above TcM. The change in Mn moments may be responsible for the change in magnetic interactions around TcM.