近日，爱尔兰都柏林圣三一大学的J. M. D.Coey及其研究团队取得一项新进展。经过不懈努力，他们揭示拓扑结构对铁磁金属相变的影响。相关研究成果已于2023年8月28日在国际知名学术期刊《美国科学院院刊》上发表。

据悉，拓扑铁磁体CoS₂在居里温度为119.8 K时表现出无磁滞效应的弱一阶跃迁，在0.034 T时表现出三临界点μ₀H_tcp。研究人员发现磁对称性和费米能级上方交叉的子带上多数和少数自旋e_g带的混合产生了磁化强度的拓扑分量，从而导致朗道自由能中负M³项的出现。费米能级相对于子带交叉的位置对于控制跃迁的阶数是至关重要的。

研究表明，在Co_0.89Fe_0.11S₂中空穴掺杂导致了少量自旋e_g袋的消耗，导致了正常的二级相变。Co_0.94Ni_0.06S₂中的电子掺杂则使费米能级向子带间隙方向升高，产生了具有15K滞后的强一阶跃迁。

这项研究结果证明了拓扑电子结构与居里点的热滞后之间的关系，这可能有助于寻找磁热材料。

附：英文原文

Title: Influence of topology on the phase transition of a ferromagnetic metal

Author: Zhang, Rui, He, Yangkun, Chen, Kaiyun, Yang, Sen, Sen, Siddhartha, Coey, J. M. D.

Issue&Volume: 2023-8-28

Abstract: The topological ferromagnet CoS₂ exhibits an anhysteretic, weakly first-order transition at the Curie temperature of 119.8 K with a tricritical point μ₀H_tcp at 0.034 T. Magnetic symmetry and the mixing of majority and minority spin e_g bands at a subband crossing just above the Fermi level produce a topological component of the magnetization that leads to a negative M³ term in the Landau free energy. The position of the Fermi level relative to the subband crossing is critical for controlling the order of the transition. Hole doping in Co_0.89Fe_0.11S₂ drains the minority-spin e_g pocket and results in a normal second-order phase transition. Electron doping in Co_0.94Ni_0.06S₂ raises the Fermi level toward the subband gap, producing a strongly first-order transition with 15 K hysteresis. Our results demonstrate a relation between topological electronic structure and thermal hysteresis at the Curie point, which may help in the search for magnetocaloric materials.

DOI: 10.1073/pnas.2302466120

Source: https://www.pnas.org/doi/10.1073/pnas.2302466120