We report on the thermoelastic properties of Ni${}_2$MnGa shape-memory alloys across the martensitic to austenitic phase transition using the time-resolved pump-probe photothermal mirror technique. Quantitative information on the thermo-mechanical characteristics of the sample are obtained and compared to specific heat measurements and differential scanning calorimetry (DSC) analysis. The thermal diffusivity varied remarkably within the martensitic-austenitic transition range. Both the amplitude signal and the thermal diffusivity present, in addition to the strong martensite to austenite phase transition, a clear evidence of a subtle second-order type phase transition close to 80 $°$C. This magnetic transition is also observed in the calorimetric analysis. The transformation temperatures suggest the non-stoichiometric composition of sample, which is also revealed by non-symmetrical shapes of DSC peaks. The possible variation of the local chemical composition could be a result of gallium loss during the sample preparation or local inhomogeneity in the martensitic transformation.

我们报道了镍的热弹性${}_2$MnGa形状记忆合金使用时间分辨泵浦探针光热镜技术跨越马氏体到奥氏体相变。获得有关样品热机械特性的定量信息，并将其与比热测量和差示扫描量热法（DSC）分析进行比较。热扩散率在马氏体-奥氏体转变范围内显着变化。除了从强马氏体到奥氏体的相变外，还存在振幅信号和热扩散率，这清楚地表明了接近80的微妙的二阶类型相变。 $°$C.在量热分析中也观察到这种磁性跃迁。转变温度表明样品具有非化学计量组成，这也由DSC峰的非对称形状揭示。局部化学成分的可能变化可能是样品制备过程中镓损失或马氏体转变中局部不均匀的结果。