Magnetic and Martensitic Transitions in Ni_2Mn_(1+x)Sn_(1-x) Alloys

摘要

The magnetic phase diagram of Ni_2Mn_(1+x)Sn_(1-x) based ferromagnetic (FM) shape memory alloys for varied concentrations of x have been studied. With increasing concentration of Mn, the FM Curie temperature (T_C) decreases, while the martensitic transition temperature (T_M) goes higher. For x = 0.44 and 0.48, T_M is close to the onset of ferromagnetism, and two distinct magnetic transitions are observed corresponding to the T_C's of the FM phases of martensite and austenite respectively. The isothermal magnetization at 5 K indicates saturating behaviour at high fields and the saturation moment drops linearly with x. The samples show reasonably large negative magnetoresistance around T_M, however the magnitude drops with increasing x. The magnetoresistance is found to be highly irreversible with respect to the applied magnetic field and field induced arrested state is observed for all the FM samples studied around the first order martensitic transition. The present investigation clearly indicates complex magnetic ground state of the Ni_2Mn_(1+x)Sn_(1-x) samples with competing magnetic interactions.