Study of relaxation phenomenon and functional properties in some ferromagnetic shape memory alloys

The effect of replacing Al with Sn in Ni2Mn1.36Sn0.64 ferromagnetic shape memory alloy was studied, with the aim of developing a system, intermediate to Sn and Al based system so that the resultant system has better functional capabilities. 
Samples were prepared using a tri-arc melting furnace. The X-ray diffraction patterns showed that the replacement of Al with Sn lead to stabilization of L21 phase in the system even in higher Al content. All samples showed martensitic transformation and it was further found that the replacement shifted the structural transformation temperature towards room temperature. 
The dynamics of the low temperature martensitic phase was studied using both ac and dc magnetization measurement technique. It was found that freezing entities were magnetic clusters rather than individual spins and freezing most probably occurred due to progressive blocking of the magnetic clusters. The dynamical study with dc magnetization in one of the system showed that it had different dynamics above internal exchange bias field. 
The magnetocaloric effect in the system was studied and it was found that Al replacement enhances these capabilities. We also showed that the measurement of MCE using indirect method of magnetization measurement agreed with more direct method of calorimetric measurements in our samples. We have also shown that magnetocaloric effect in the system can be tuned by giving proper secondary heat treatment either at low or high temperature. Also the secondary heat treatment influenced the magnetic cluster size. The replacement and secondary heat treatment thus offer a way to enhanced and tune the magnetocaloric property of these systems.