The influence of hydrostatic pressure and annealing conditions on the magnetostructural transitions in MnCoGe
The influence of hydrostatic pressure and annealing conditions on the magnetostructural transitions in MnCoGe
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DOI：
10.1063/5.0053671
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发表时间：
2021-06-07
影响因子：
3.2
通讯作者：
Stadler, Shane
中科院分区：
文献类型：
--
作者：
Chen, Jing-Han;Poudel Chhetri, Tej;Stadler, Shane
在这项工作中，通过系统地改变退火条件和施加静水压力，化学计量比MnCoGe合金的相变进行了研究。从Ni 2 In型六方奥氏体相到TiNiSi型正交马氏体相的一级马氏体结构转变跨越宽的温度窗口（0.200 K），这是由于在从700摄氏度的固相到1150摄氏度的液相的温度范围内淬火样品。尽管它们的结构转变温度变化很大，但在结构转变过程中的晶胞参数变化和马氏体/奥氏体相的居里-外斯温度相对较小。对于从800摄氏度淬火的样品，观察到耦合的磁结构转变，并且发现对于7 T场变化，最大的最大磁熵变为Δ S-max = 33.6 J/kg K。耦合的磁结构转变和相应的磁熵增强被发现也可以通过施加静水压力来实现。同时，随着淬火温度或静水压力的增加，一级马氏体结构转变向低温移动，直到它最终消失，在这种情况下，只有Ni 2 In型六方奥氏体相的晶体结构和磁性转变。
In this work, the phase transitions of stoichiometric MnCoGe alloys were studied by systematically varying the annealing conditions and applying hydrostatic pressure. First-order martensitic structural transitions from the Ni2In-type hexagonal austenite phase to the TiNiSi-type orthorhombic martensite phase spanned a wide temperature window (.200 K) as a result of quenching the samples at temperatures ranging from the solid phase at 700 degrees C to the liquid phase at 1150 degrees C. Despite the large variation in their structural transition temperatures, the changes in cell parameters across the structural transitions and the Curie-Weiss temperatures of the martensite/austenite phase were relatively small. For the sample quenched from 800 degrees C, coupled magnetostructural transitions were observed, and the largest maximum magnetic entropy change was found to be Delta S-max = 33.6 J/kg K for a 7-T field change. The coupled magnetostructural transitions and the corresponding magnetic entropy enhancements were found to also be achievable by applying hydrostatic pressures. Meanwhile, as the quenching temperatures or hydrostatic pressures increased, the first-order martensitic structural transition shifted toward lower temperature until it was ultimately absent, in which case only the crystal structure and magnetic transition of the Ni2In-type hexagonal austenite phase were present.