Ni-Mn基铁磁形状记忆合金的低温相分离和交换偏置效应研究

Ni-Mn-based ferromagnetic shape memory alloys have attracted much attention due to their abundant physical properties and potential application in actuator, sensor, and magnetic refrigeration. In our previous investigations, it has been found that the exchange bias field is associated with the value of magnetization (the proportion of ferromagnetic phase), and the exchange bias effect in Ni-Mn-Ga alloy was first observed. In this project, we aim to further understand the physical mechanism of the exchange bias effect in Ni-Mn-based ferromagnetic shape memory alloys, and the coupling mechanism between ferromagnetic and antiferromagnetic phase. We plan to investigate the magnetism, spin-glass-like behavior, and exchange bias effect, disclose the relation between phase proportion, spin-glass-like behavior, and exchange bias effect, and the origin and physical nature of zero-field-cooled exchange bias effect. We will also investigate the factors that influence the exchange bias effect, such as magnetic field and temperature. In addition, we will try to develop Ni-Mn-Ga and Ni-Mn-Al alloys having exchange bias effect.

近年来，Ni-Mn基铁磁形状记忆以其丰富的物理内涵和潜在的应用前景，成为材料物理领域的一个研究热点。我们的前期工作发现：在Ni-Mn基合金中，交换偏置场大小和低温饱和磁化强度(即铁磁相比例)相关，并首次在Ni-Mn-Ga体系中发现了交换偏置效应。为深入理解Ni-Mn基铁磁形状记忆合金中交换偏置效应的内在机制，铁磁和反铁磁相(或者自旋玻璃)之间的耦合机理，以更好地对交换偏置效应进行调控，本项目拟从Ni-Mn基合金的低温铁磁相比例调节入手，系统研究合金的磁性、类自旋玻璃行为和交换偏置现象，揭示相比例、类自旋玻璃行为和偏置效应的相互关联，阐明零场冷交换偏置效应的产生条件和物理本质；研究磁场(冷却场、磁滞回线最大磁场)、温度等因素对交换偏置效应的影响规律；开发具有交换偏置效应的Ni-Mn-Ga和Ni-Mn-Al基合金材料。

Ni-Mn基铁磁形状记忆合金以其丰富的物理内涵和潜在的应用前景，成为材料物理领域的一个研究热点。除了马氏体转变附近的丰富的物理现象，铁磁和反铁磁交换作用的共存和竞争产生了复杂的磁性基态和交换偏置，包括传统的场冷交换偏置和最近发现的零场冷交换偏置效应。本项目主要围绕着Ni-Mn基铁磁形状记忆合金在低温下的交换偏置下应展开研究，研究了材料的低温磁性和交换偏置的影响因素，如通过调整Mn/Ga比例研究对Ni-Mn-Ga合金的磁性和交换偏置效应的影响，在非正分的Ni-Mn-Ga体系中发现了零场冷交换偏置效应；在Ni-Mn-Sn合金中研究了贵金属Pt(Pd)掺杂对低温磁性和交换偏置的影响，提出具有强自旋轨道耦合的原子的掺杂有助于增强交换偏置效应；采用磁电阻测量的方法对Mn-Ni-Sn合金的交换偏置效应进行了探测，发现磁电阻效应是探测磁基态和交换偏置效应的有效方法；研究了晶格大小的调控对低温磁性和交换偏置的影响，比如在Ni-Mn-Sb合金中通过Al替代Sb，发现小原子的替代可以增强反铁磁交换作用，并首次在Ni-Mn-Sb基合金中实现了零场冷交换偏置效应。更为重要的是，我们通过系统研究二元Ni-Mn合金的磁相图和交换偏置效应，发现零场冷交换偏置效应在多临界点附近出现，这个结果为我们寻找具有零场冷交换偏置效应的材料体系提供了思路。