Phase Competition in the Palmer-Chalker XY Pyrochlore Er2Pt2O7
Phase Competition in the Palmer-Chalker XY Pyrochlore Er2Pt2O7
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DOI：
10.1103/physrevlett.119.187201
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发表时间：
2017-10-30
影响因子：
8.6
通讯作者：
Gaulin, B. D.
中科院分区：
文献类型：
--
作者：
Hallas, A. M.;Gaudet, J.;Gaulin, B. D.
我们报告了 Er2Pt2O7 的中子散射测量结果，Er2Pt2O7 是 XY 系列受挫烧绿石磁体的新成员。我们的弹性散射数据的对称分析表明，Er2Pt2O7 在 T-N = 0.38 K 时有序化为 k = 0、Gamma(7) 磁结构（Palmer-Chalker 态）。这与其姊妹 XY 烧绿石反铁磁体 Er2Ti2O7 和 Er2Ge2O7 形成对比，这两种磁体均在更高的温度下有序化为 Gamma(5) 磁结构（T-N = 1.2 和分别为 1.4 K。在此温度范围内，Er2Pt2O7 的磁热容包含以 T* = 1.5 K 为中心的广泛异常。我们的非弹性中子散射测量表明，这种广泛的热容异常为强短程自旋波动设定了温度尺度。在 T-N = 0.38 K 以下，Er2Pt2O7 显示带隙自旋波谱，在较低能量下具有强烈、平坦的激发带，在较高能量下具有弱、扩散的激发带。经典的自旋波计算很好地描述了平带，但这些计算也预测了较高能量下的尖锐色散分支，这与实验数据存在惊人的差异。这与 T-N 的强烈抑制相一致，可归因于经典预测相图中彼此相邻的 Gamma(7) 和 Gamma(5) 态之间的相位竞争导致量子涨落增强。
We report neutron scattering measurements on Er2Pt2O7, a new addition to the XY family of frustrated pyrochlore magnets. Symmetry analysis of our elastic scattering data shows that Er2Pt2O7 orders into the k = 0, Gamma(7) magnetic structure (the Palmer-Chalker state), at T-N = 0.38 K. This contrasts with its sister XY pyrochlore antiferromagnets Er2Ti2O7 and Er2Ge2O7, both of which order into Gamma(5) magnetic structures at much higher temperatures, T-N = 1.2 and 1.4 K, respectively. In this temperature range, the magnetic heat capacity of Er2Pt2O7 contains a broad anomaly centered at T* = 1.5 K. Our inelastic neutron scattering measurements reveal that this broad heat capacity anomaly sets the temperature scale for strong short-range spin fluctuations. Below T-N = 0.38 K, Er2Pt2O7 displays a gapped spin-wave spectrum with an intense, flat band of excitations at lower energy and a weak, diffusive band of excitations at higher energy. The flat band is well described by classical spin-wave calculations, but these calculations also predict sharp dispersive branches at higher energy, a striking discrepancy with the experimental data. This, in concert with the strong suppression of T-N, is attributable to enhanced quantum fluctuations due to phase competition between the Gamma(7) and Gamma(5) states that border each other within a classically predicted phase diagram.