Abstract Using surface acoustic waves (SAW) the elastic properties of 500 nm thick epitaxial off-stoichiometric Ni-Mn-Ga films prepared by sputtering on MgO substrate were determined in a broad temperature range both in austenite and martensite and across the martensitic transformation. At room temperature the films were in non-modulated martensite with tweed-like microstructure. Structural and magnetic studies proved that the martensitic structure can be considered homogenous on the scale of surface waves owing to the fine twinning. Measured angular dependence of SAW velocities indicated that the averaged in-plane tetragonal structure can be used for the calculation of elastic coefficients in martensite. The phase velocity of SAW showed an anomaly around the phase transition temperature due to changes of the shear elastic coefficients, c ' and c 44 . During cooling there was a gradual softening of c ' in austenite. The softening turned to stiffening at the onset of the martensitic transformation while c 44 sharply decreased. The shear coefficients for martensite and paramagnetic austenite of the film are comparable to Ni-Mn-Ga bulk single crystal. No significant effect of magnetic field on elastic coefficients was detected in agreement with the bulk.

中文翻译：

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Ni-Mn-Ga外延膜的奥氏体和马氏体弹性性能的温度依赖性

摘要 使用表面声波 (SAW)，在奥氏体和马氏体以及整个马氏体相变的宽温度范围内测定了通过溅射在 MgO 衬底上制备的 500 nm 厚外延非化学计量 Ni-Mn-Ga 薄膜的弹性特性。在室温下，薄膜处于具有花呢状微观结构的非调制马氏体中。结构和磁性研究证明，由于精细孪晶，马氏体结构在表面波尺度上可以被认为是均匀的。测量的 SAW 速度的角度相关性表明平均面内四方结构可用于计算马氏体中的弹性系数。由于剪切弹性系数 c ' 的变化，SAW 的相速度在相变温度附近表现出异常 和 c 44。在冷却过程中，奥氏体中的 c ' 逐渐软化。在马氏体转变开始时，软化转为硬化，而 c 44 急剧下降。该膜的马氏体和顺磁性奥氏体的剪切系数与 Ni-Mn-Ga 块状单晶相当。与块体一致，未检测到磁场对弹性系数的显着影响。