We investigate relative stability, structural properties and electronic structure of various modulated martensites of the magnetic shape memory alloy Mn$_{2}$NiGa by means of density functional theory. We observe that the instability in the high-temperature cubic structure first drives the system to a structure where modulation shuffles with a period of six atomic planes are taken into account. The driving mechanism for this instability is found to be the nesting of the minority band Fermi surface, in a similar way as established for the prototype system Ni$_{2}$MnGa. In agreement with experiments, we find 14M modulated structures with orthorhombic and monoclinic symmetries having energies lower than other modulated phases with same symmetry. In addition, we also find energetically favourable 10M modulated structures which have not been observed experimentally for this system yet. The relative stability of various martensites is explained in terms of changes in the electronic structures near the Fermi level, affected mostly by the hybridisation of Ni and Mn states. Our results indicate that the maximum achievable magnetic field-induced strain in Mn$_{2}$NiGa would be larger than in Ni$_{2}$MnGa. However, the energy costs for creating nanoscale adaptive twin boundaries are found to be one order of magnitude higher than that in Ni$_{2}$MnGa.
A high resolution synchrotron x-ray powder diffraction study of the incommensurate modulation in the martensite phase of Ni2MnGa: Evidence for nearly 7M modulation and phason broadening
Adaptive modulation in Ni2Mn1.4In0.6 magnetic shape memory Heusler alloy
Ni-Mn基Heusler型磁性记忆合金（MSMAs）中的无公度结构调制是磁场诱导超高应变的重要原因之一。在原型MSMA Ni 2 MnGa中，观察到原子从调制马氏体相、预马氏体相和电荷密度波中的平均位置的非均匀位移以及卫星峰的相子展宽，以支持与软声学声子相关联的电子不稳定性模型。本文采用（3+1）D超空间群方法对Ni_2Mn_（1.4）In_（0.6）合金进行了高分辨同步辐射X射线粉末衍射（SXRPD）和中子粉末衍射（NPD）研究。其不仅揭示了在低温下在反铁磁相中具有物理上可接受的有序磁矩的马氏体相的调制结构中的均匀原子位移，预马氏体相和卫星峰的相子展宽。我们的高分辨透射电镜研究和基态的第一性原理计算也支持粉末衍射研究预测的均匀原子位移。所有这些观察表明，在马氏体相的Ni2Mn1.4In0.6 MSMA的结构调制可以解释的自适应相模型。本研究强调了使用互补SXRPD和NPD的超空间群分析的重要性，在理解调制的起源以及Heusler型MSMA的磁和调制基态的物理。我们的工作还强调了这样一个事实：不同Ni-Mn基MSMA中调制结构起源的机制可能并不普遍，必须在不同的合金成分中进行彻底的研究。
First-principles study of doping influence on twin formation in Ni-Mn-Ga nonmodulated martensite
Institute of Thermomechanics of the Czech Academy of Sciences（捷克科学院热力学研究所）；Institute of Physical Engineering, Faculty of Mechanical Engineering, Brno University of Technology（布尔诺理工大学机械工程学院物理工程研究所）；Faculty of Metals Engineering and Industrial Computer Science, AGH University of Krakow（克拉科夫AGH大学金属工程与工业计算机科学学院）；FZU - Institute of Physics of the Czech Academy of Sciences（捷克科学院物理学研究所（FZU））；Tikomat Ltd.（Tikomat有限公司）；Institute of Materials Science and Engineering, Faculty of Mechanical Engineering, Brno University of Technology（布尔诺理工大学机械工程学院材料科学与工程研究所）
