First-order ferromagnetic transitions of lanthanide local moments in divalent compounds: An itinerant electron positive feedback mechanism and Fermi surface topological change
First-order ferromagnetic transitions of lanthanide local moments in divalent compounds: An itinerant electron positive feedback mechanism and Fermi surface topological change
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DOI：
10.1103/physrevb.101.174437
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发表时间：
2020-05
影响因子：
3.7
通讯作者：
E. Mendive-Tapia;D. Paudyal;L. Petit;J. Staunton
中科院分区：
文献类型：
--
作者：
E. Mendive-Tapia;D. Paudyal;L. Petit;J. Staunton
在不连续（一阶）磁相变附近，材料对小磁场的强热响应被广泛研究，以发展固态制冷。通常，强磁结构耦合驱动这样的转变，并且伴随的显著滞后显著地降低冷却性能。在这种情况下，我们描述了一个纯粹的电子机制，飞行员的一阶顺磁-铁磁转变的二价镧系化合物，并解释了巨大的非滞后磁热效应最近发现的Eu $_2 $In化合物。巡游价电子的磁性与局域f电子磁矩的铁磁有序性之间存在正反馈，表现为费米面的拓扑变化。这种电子机制的起源直接源于Eu的二价性，这解释了Gd$_2$In中没有类似的不连续跃迁。
Around discontinuous (first-order) magnetic phase transitions the strong caloric response of materials to the application of small fields is widely studied for the development of solid-state refrigeration. Typically strong magnetostructural coupling drives such transitions and the attendant substantial hysteresis dramatically reduces the cooling performance. In this context we describe a purely electronic mechanism which pilots a first-order paramagnetic-ferromagnetic transition in divalent lanthanide compounds and which explains the giant non-hysteretic magnetocaloric effect recently discovered in a Eu$_2$In compound. There is positive feedback between the magnetism of itinerant valence electrons and the ferromagnetic ordering of local $f$-electron moments, which appears as a topological change to the Fermi surface. The origin of this electronic mechanism stems directly from Eu's divalency, which explains the absence of a similar discontinuous transition in Gd$_2$In.