铁磁形状记忆合金Mn_2NiGa中应力诱发马氏体相的结构和磁性

Structure and magnetic properties of stress-induced martensites in ferromagnetic shape memory alloy Mn_2NiGa

采用金刚石对顶砧高压装置(DAC)和同步辐射X射线光源法,对Heusler类型的磁性形状记忆合金Mn2NiGa的结构进行了原位高压X射线衍射测量,并对卸载后的受压样品进行了磁测量.实验观察到材料在室温下分别在0.77GPa和20GPa压力下发生了两次不可逆结构相变:马氏体相变和两种不同马氏体间的等结构相变.同时加压使马氏体结构中产生了大量的缺陷,造成了严重的晶格畸变,致使马氏体结构的矫顽力提高了近10倍,达到204kA/m.结果发现,加压处理造成样品马氏体相饱和磁化强度的大幅度降低,显示出明显的缺陷效应.

In-situ high pressure X-ray diffraction experiments on Heusler-type ferromagnetic shape memory alloy Mn2NiGa under pressure up to 40 GPa have been carried out by using diamond anvil cell device with synchrotron radiation source, and magnetic measurements have also been performed on uninstalled samples by using vibration sample magnetometer. At ambient pressure Mn2 NiGa has body centered cubic structure. Two phase transitions in Mn2 NiGa were observed during high pressure experiments. The first at about 0.77 GPa is belong to martensitic transformation, and the second at about 20 GPa is isostructural transformation between two different martensites. Meanwhile, a lot of defects and distortion of lattice were generated in martensites due to pressurization. Consequently, coercive force of stress-induced martensites rises up to 204 kA/m and it is almost ten times larger than that of thermo-induced martensites. Pressure processes also make saturation magnetization of martensites decrease rapidly, which reveals the obvious defect effect.