Zhang Le, Zhang Ji, Li Kaili, Zhou Chao, Yao Yin, Tan Thiam Teck, Wang Danyang, Yang Sen, Li Sean, Carpenter Michael A
School of Materials Science and Engineering, UNSW Sydney, Sydney, NSW 2052, Australia.
School of Science and MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi'an Jiaotong University, Xi'an 710049, China.
ACS Appl Mater Interfaces. 2020 Sep 30;12(39):43646-43652. doi: 10.1021/acsami.0c11308. Epub 2020 Sep 15.
In this work, the structural and magnetic transitions of Heusler alloy NiMnInGa have been carefully studied through measurements of heat flow and magnetization under DC and AC magnetic fields. This alloy undergoes the transition sequence of spin-glassy martensite (SPM) → ferromagnetic austenite (FA) → paramagnetic austenite at ∼225 and ∼305 K, respectively, during heating. Splitting of zero-field-cooling (ZFC)/field-cooling (FC) curves in martensite is caused by the slowdown dynamics of spin glass as evidenced by frequency dispersion and aging effects. The development of a spin-glass state is believed to be the result of strain relaxation and interaction of ferroelastic twin walls in the martensite. The magnetocaloric effect (MCE) at the SPM-FA transition was then measured using indirect, quasi-direct, and direct methods. The MCE magnitudes are controlled by the entropy changes associated with the first-order martensite transition and magnetic ordering of austenite under the magnetic field. The existence of a spin-glass state in martensite can also improve the reversibility of the magnetostructural transitions, which is beneficial for the improvement of the reversibility of associated MCE. These results provide an in-depth understanding of the transitions and magnetic properties of the Ni-Mn Heusler alloys and suggest that the MCE at the first-order magnetostructural transitions estimated solely using indirect methods may need some revision.
在这项工作中，通过在直流和交流磁场下测量热流和磁化强度，对赫斯勒合金NiMnInGa的结构和磁性转变进行了仔细研究。在加热过程中，该合金分别在约225 K和约305 K经历自旋玻璃态马氏体（SPM）→铁磁奥氏体（FA）→顺磁奥氏体的转变序列。马氏体中零场冷却（ZFC）/场冷却（FC）曲线的分裂是由自旋玻璃动力学减慢引起的，频率色散和时效效应证明了这一点。自旋玻璃态的形成被认为是马氏体中应变弛豫和铁弹孪晶界相互作用的结果。然后使用间接、准直接和直接方法测量了SPM-FA转变处的磁热效应（MCE）。MCE的大小由与一级马氏体转变和磁场下奥氏体的磁有序相关的熵变控制。马氏体中自旋玻璃态的存在还可以提高磁结构转变的可逆性，这有利于相关MCE可逆性的提高。这些结果深入了解了Ni-Mn赫斯勒合金的转变和磁性，并表明仅使用间接方法估计的一级磁结构转变处的MCE可能需要一些修正。
