Magnetic properties and magnetostructural phase transitions in Ni_2+xMn_1−xGa shape memory alloys

A systematic study of magnetic properties of Ni_2+xMn_1−xGa (0≤x≤0.19) Heusler alloys undergoing structural martensite-austenite transformations while in the ferromagnetic state has been performed. From measurements of spontaneous magnetization, M_s(T) , jumps ΔM at structural phase transitions were determined. Virtual Curie temperatures of martensite were estimated from the comparison of magnetization in martensitic and austenitic phases. Both saturation magnetic moments in the ferromagnetic state and effective magnetic moments in paramagnetic state of Mn and Ni atoms were estimated and the influence of delocalization effects on magnetism in these alloys was discussed. The experimental results obtained show that the shift of martensitic transition temperature depends weakly on composition. The values of this shift are in good correspondence with the Clapeyron-Clausius formalism taking into account the experimental data on latent heat at martensite-austenite transformations.