Thermal and transport properties of Ni2MnGa1−xAlx alloys

A series of Ni2MnGa1−xAlx (x = 0, 0.03, 0.05, 0.10, 0.15 and 0.20) alloys are studied by means of electrical resistivity, ρ(T), Seebeck coefficient, S(T), thermal conductivity, κ(T), as well as specific heat measurements. It is observed that the martensitic transition temperature show a significant but complex variation for the low level of partial Al substitution with respect to Ga whereas magnetic ordering temperature is little affected. However, upon increasing Al content (x ≥ 0.10), a drastic suppression of the martensitic transition along with a gradual broadening/suppression of the magnetic ordering take place. Such observations are in sharp contrast to the general expectation for the nonmagnetic and isoelectronic Al substitution with respect to Ga. X-ray diffraction studies revealed that increase in Al substitution leads to the formation of B2 phase and which plays an important role on the martensitic and magnetic transition characteristics and physical properties of Ni2MnGa1−xAlx alloys.