Ni2Mn1-yZy(Z = In,Sn 和Sb）铁磁形状记忆合金的磁熵研究

Ni2Mn1-yZy（Z = In, Sn and Sb）is a new type of ferromagnetic shape memory alloys (FSMAs) and possesses the magnetic-field-induced Martensitic transformation in which the giant thermoelastic, magnetoelastic, magnetoresistance and magnetocaloric effects are taking place simultaneously. The magnetocaloric value in theory can reach as high as 90 J/kg K and is almost 2-3 times as that can be obtained in laboratory. However, it is not yet applied in industry even though Ni2Mn1-yZy is considered as the best choice for using as smart functional material in the future because some basic physical problems are still not resolved, which provents this material from application in reality. In this project, after fitting Cp - T experimental curves, the contributions of entropy from spin, electron, lattice and crystal field effect shall be separated for Ni2Mn1-yZy in different phase regions and during the field-induced Martensitic transformation. Resonable methods will be proposed in order to enhance the magnetocaloric effect after the analysis of entropy separation. In addition, high pulse magnetic field will be performed to study the magnetic induced the intermartensitic transformation and magnetic entropy changes for Ni2Mn1-yZy alloys. The research is expected to be original, valubale and significant for understanding the magnetic properties of FSMAs deeply and widely since the ideas and methods refered in this proposal were seldom applied to explore in the past years.

Ni2Mn1-yZy（Z = In、Sn 和Sb）是一类新型铁磁形状记忆合金（FSMAs），具有磁诱导马氏体相变，并伴随有巨热弹、磁弹、磁电阻和磁熵变等新奇的物理效应，理论磁熵变高达90 J/kg K,是目前FSMAs 在实验室所能获得最高值的近2-3 倍（H = 5 T）。其低温马氏体相还存在自旋极化、磁矩量子化及交换偏置现象。该合金虽是智能化优选材料，但由于一些物理机制没有完全解决，阻碍了其走向实际应用。本项目利用Cp - T 实验曲线及曲线拟合将自旋、电子、晶格和晶场作用等因素对Ni2Mn1-yZy 在不同相区以及磁诱导马氏体相变中的熵变贡献进行剥离，提出增大磁熵变的科学方法。利用脉冲强磁场在强场条件下研究其中间马氏体相变及磁熵变。由于这些观点和方法在过去FSMAs 研究中较少涉及和使用，该研究具有较大原始创新性，对拓宽和加深理解FSMAs 的磁性和磁熵变具有一定价值和意义。

Ni2Mn1-yZy（Z = In、Sn 和Sb）是一类新型铁磁形状记忆合金（FSMAs），具有磁诱导马氏体相变、预马氏体相变，并伴随有巨热弹、磁弹、磁电阻和磁熵变等新奇的物理效应，是目前磁学及磁性材料研究热点和前沿之一。该材料理论磁熵变高达90 J/kg K,是目前商用室温磁制冷材料Gd的10.2J/kg K（H = 50 kOe）的8倍，但其较低的巨磁熵变温度（《300 K），较窄的磁熵变温区（10 - 20 K）和较高磁场（H 〉5.0 T）限制了该材料的实际应用。本项目从理论和实验两方面研究了NiMn基铁磁形状记忆合金的磁性起源及磁性与结构之间的关系，着重研究了外加磁场，磁场诱导马氏体相变对该材料体系磁熵变的影响，探索了提高马氏体相变点，磁熵变值拓宽磁熵变温区的方法。发现少量Al替代可大幅提高该材料体系的相变温度和磁熵变值，Ni50Mn34In15Al 在室温附近和较宽温度窗口（280 – 310 K）存在磁诱导一级马氏体相变和顺磁 - 铁磁二级磁相变，磁熵变分别为21.3 J/kg K和8.2 J/kg K (50 kOe) , 相应制冷效率分别为152.3 J/kg和157.9 J/kg，磁熵变和制冷效率分别是目前商用室温磁制冷材料Gd的3倍和4倍，是一种具有实际应用前景的室温磁制冷材料。此外在脉冲强磁场条件下，利用光学显微镜在该材料体系直接观察到从立方奥氏体到四方马氏体结构的相变过程以及在奥氏体磁性相变与马氏体相变之间存在预马氏体相变。