Understanding modulated Phases in Heusler Alloys

调制相似乎是各种功能材料的普遍特征。特别是对于Ni-Mn-Ga Heusler合金，在外加磁场作用下，14M调制马氏体形变达到最大应变，接近10%。最近，我们发现这种相可以由非调制(NM)马氏体相的纳米孪晶变体按照自适应马氏体相的概念构建。与分支相结合，这一概念提出了对这一相的关键特征的微观解释。在这里，我们旨在了解在Heusler合金中观察到的与成分、温度、应力和磁场有关的不同调制相的起源。用外延膜和大块单晶的形式研究了Ni-Mn-Ga和其他Heusler合金的结构和相变。由于调制结构影响材料从原子到宏观长度尺度，专用的积分衍射法与高分辨率局部探头相结合被应用。最后分析了调制对Heusler合金功能性能的影响。

Modulated phases seem to be a general feature of various functional materials. In particular for Ni-Mn-Ga Heusler alloys, the 14M modulated martensite reaches the highest strain close to 10% in external magnetic fields. Recently we showed that this phase can be built from nanotwinned variants of the non-modulated (NM) martensite phase following the concept of adaptive martensite. In combination with branching this concept suggests microscopic explanations of the key features of this phase.Here we aim to understand the origin of the differently modulated phases observed in Heusler alloys in relation to composition, temperature, stress and magnetic fields. Structure and phase transformation of Ni-Mn-Ga and other Heusler alloys are examined in form of epitaxial films and bulk single crystals. Since modulated structures affect the material from the atomistic to the macroscopic length scale, dedicated integral diffraction methods in combination with high resolution local probes are applied. Finally consequences of the modulation for the functional properties of Heusler alloys are analyzed.