稀土元素La在MnCoGe体系中的掺杂效应

Effect of doping with rare-earth element La in MnCoGe system

MnCoGe是MM′X型马氏体相变材料体系中最具代表性的研究对象之一.由于其结构相变温度高于自身的磁有序温度,研究者采用了各种调控方法来降低结构相变温度以实现磁共结构耦合.但是,针对稀土元素在这类体系中的掺杂效应较少被报道.因此,本文研究了Mn_(1-x)La_(x)CoGe (x=0, 0.01, 0.02, 0.03, 0.05)系列化合物的结构与磁性. La的加入引起主相中Mn和Ge元素的成分缺失,使得马氏体转变温度逐渐降低,实现了磁共结构耦合.然而,由于La导致元素成分缺失的能力有限,进一步增加掺杂量导致析出更多的第二相但却没有引起相变温度的持续降低.在微观组织中观察到主相被针状第二相分隔成小"畴",这可能是高La含量样品中存在大量残余奥氏体相的原因.

MnCoGe is one of the most representative materials that undergoes martensitic transformation in the MM′X system.Because the phase transition temperature of MnCoGe is higher than its magnetic ordering temperature, various methods have been used to decrease the phase transition temperature and realize magneto-structural coupling. However, there are rare reports about the effect of doping with rare-earth elements. In this work, the structures and physical properties of Mn_(1-x)La_(x)CoGe compounds with x=0, 0.01, 0.02, 0.03, and 0.05 were studied. The introduction of La causes a deficiency of both Mn and Ge atoms in the main phase, which leads to a decrease in the martensitic transformation temperature and the realization of magneto-structural coupling. However, due to its limited ability of deficiency formation, a further increase in the La content leads to large amount of secondary phase instead of a continuous decrease of the phase transition temperature. Additionally, the MnCoGe matrix is found to be divided into small "domains" by the needle-like secondary phase, which is the reason for the large amount of retained austenite phase in the sample with a high La content.