近日，美国爱荷华州立大学的Paul C. Canfield&Sergey L. Bud’ko及其研究小组与加拿大麦吉尔大学的Dominic H. Ryan等人合作并取得一项新进展。经过不懈努力，他们揭示高压下EuPd₃S₄中的磁序温度增强和结构/价态跃迁现象。相关研究成果已于2023年12月19日在国际知名学术期刊《美国科学院院刊》上发表。

本文通过电输运、X射线衍射、时域¹⁵¹Eu同步加速器穆斯堡尔光谱和高压下的X射线吸收光谱测量，对非均匀混合价化合物EuPd₃S₄进行了全面的研究。电输运测量表明，反铁磁序温度T_N从环境压力下的2.8 K迅速上升到约19 GPa时的23.5 K，并在约19 到29 GPa之间达到峰值，之后没有发现与T_N相关的异常。研究人员观察到压力诱导的一阶结构相变，从立方到四方，具有相当宽的共存区域(约 20gpa 到30gpa)，对应于T_N平台。

穆斯堡尔谱测量表明，在约28 GPa下，Eu²⁺与Eu³⁺的价态从约50:50转变为完全的Eu³⁺，这与相同压力下磁序的消失一致。X射线吸收数据显示在类似压力下跃迁到完全三价态。这项研究结果表明，压力首先极大地增强了T_N，很可能是通过增强Eu 4f态和导带之间的杂化。随后，压力导致了结构相变，与铕向完全三价态的跃迁相一致。

附：英文原文

Title: Strong enhancement of magnetic ordering temperature and structural/valence transitions in EuPd₃S₄ under high pressure

Author: Huyan, Shuyuan, Ryan, Dominic H., Slade, Tyler J., Lavina, Barbara, Jose, Greeshma, Wang, Haozhe, Wilde, John M., Ribeiro, Raquel A., Zhao, Jiyong, Xie, Weiwei, Bi, Wenli, Alp, Esen E., Bud’ko, Sergey L., Canfield, Paul C.

Issue&Volume: 2023-12-19

Abstract: We present a comprehensive study of the inhomogeneous mixed-valence compound, EuPd₃S₄, by electrical transport, X-ray diffraction, time-domain ¹⁵¹Eu synchrotron Mssbauer spectroscopy, and X-ray absorption spectroscopy measurements under high pressure. Electrical transport measurements show that the antiferromagnetic ordering temperature, T_N, increases rapidly from 2.8 K at ambient pressure to 23.5 K at ~19 GPa and plateaus between ~19 and ~29 GPa after which no anomaly associated with T_N is detected. A pressure-induced first-order structural transition from cubic to tetragonal is observed, with a rather broad coexistence region (~20 GPa to ~30 GPa) that corresponds to the T_N plateau. Mssbauer spectroscopy measurements show a clear valence transition from approximately 50:50 Eu²⁺:Eu³⁺ to fully Eu³⁺ at ~28 GPa, consistent with the vanishing of the magnetic order at the same pressure. X-ray absorption data show a transition to a fully trivalent state at a similar pressure. Our results show that pressure first greatly enhances T_N, most likely via enhanced hybridization between the Eu 4f states and the conduction band, and then, second, causes a structural phase transition that coincides with the conversion of the europium to a fully trivalent state.

DOI: 10.1073/pnas.2310779120

Source: https://www.pnas.org/doi/abs/10.1073/pnas.2310779120