Spin ordering induced by lattice distortions in classical Heisenberg antiferromagnets on the breathing pyrochlore lattice
Spin ordering induced by lattice distortions in classical Heisenberg antiferromagnets on the breathing pyrochlore lattice
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DOI：
10.1103/physrevb.99.144406
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发表时间：
2019-04-05
影响因子：
3.7
通讯作者：
Kawamura, Hikaru
中科院分区：
文献类型：
--
作者：
Aoyama, Kazushi;Kawamura, Hikaru
我们从理论上研究了晶格畸变对呼吸烧绿石晶格上经典海森堡反铁磁体自旋有序的影响。在该模型中，考虑到从网站振动产生有效的自旋相互作用，通过自旋晶格耦合（SLC）的本地晶格畸变。呼吸晶格交替的特点是最近邻相互作用的比例为大的四面体，为小的，J '/J。它是由Monte Carlo模拟发现，该系统表现出一级过渡到四种不同类型的共线磁有序态。在均匀情况下（J '/J = 1），在较强SLC下实现的态是以（1/2，1/2，1/2）磁布拉格峰为特征的对称态，而在较弱SLC下实现的态是以（1，1，0）磁布拉格峰为特征的四方对称态。随着呼吸畸变的增加（J '/J减小），（1/2，1/2，1/2）态的有序模式变为非立方，其磁布拉格反射几乎不变，而（1，1，0）态是稳健的。呼吸式火成石所特有的非立方状态可进一步分为两类。我们证明了这两种非立方序导致基态的大质量简并，并且每自旋的相关剩余熵取类似或等于ln（4）/16 k（B）和类似或等于ln（6）/16 k（B）的特征值.实验结果的影响进行了讨论。
We theoretically investigate effects of lattice distortions on the spin ordering of classical Heisenberg antiferromagnets on the breathing pyrochlore lattice. In the model, local lattice distortions originating from the site vibration are taken into account to yield effective spin interactions via the spin-lattice coupling (SLC). The breathing lattice alternation is characterized by the ratio of the nearest-neighbor interaction for large tetrahedra to that for small ones, J'/J. It is found by Monte Carlo simulations that the system exhibits a first-order transition into four different types of collinear magnetic ordered states. In the uniform case (J'/J = 1), the state realized at stronger SLC is cubic-symmetric characterized by the (1/2, 1/2, 1/2) magnetic Bragg peaks, while the one at weaker SLC is tetragonal-symmetric characterized by the (1,1,0) ones. With increasing the breathing distortion (decreasing J'/J), the ordering pattern of the (1/2, 1/2, 1/2) state becomes noncubic with its magnetic Bragg reflections almost unchanged, while the (1,1,0) state is robust. The noncubic state peculiar to the breathing pyrochlores is further categorized into two types. We demonstrate that these two noncubic orderings result in the massive degeneracy of the ground state and that the associated residual entropy per spin takes characteristic values of similar or equal to ln(4)/16k(B) and similar or equal to ln(6)/16k(B). Experimental implications of the results are discussed.