Revival of martensitic instability in Ga doped Ni-Mn-In alloys

We report here the results of transport and dc magnetization studies of Ga-doped Ni2Mn1.32In0.68 (Ni2Mn1.32In0.68−xGax, x = 0, 0.04, 0.08, 0.16, 0.20, and 0.28) alloys. The parent sample (x = 0) does not show any structural instability, however small Ga substitution at the In site (x = 0.08) suddenly induces martensitic transition in it. The studied alloys are all found to be ferromagnetic below about room temperature and the martensitic transition temperatures are found to be in the range between 175 K and 240 K depending upon x. Samples showing thermally driven maretnsitic transition (x≥ 0.08) are also found to be susceptible to the applied magnetic field, and both magnetization and magnetoresistance indicate the signature of field-induced transition. Upon cooling under a magnetic field, we observe kinetically arrested state which is particularly prominent in low Ga containing samples (x = 0.08, 0.16). It clearly demonstrate that these Ga doped samples posses all the properties of metamagnetic shape memory alloys. We argue that the magnetically arrested state in the alloys is closely connected to the competition between chemical and magnetic free energies associated with the martensitic and austenitic phases.