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Continuous magnetic phase transition in half-frustrated Ca_2O_s2O_7

机译：半挫折的Ca_2O_s2O_7中的连续磁相变

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摘要

We present the specific heat, magnetization, optical spectroscopy measurements, and the first-principles calculations on the Weberite structure Ca_2O_s2O_7 single-crystal/polycrystalline sample. The Ca_2O_s2O_7 shows a Curie-Weiss nature at high temperature and goes into a ferrimagnetic insulating state at 327 K on cooling. A X-like peak is observed at 327 K in the specific heat implying a second-order phase transition. The vanishing electronic specific heat at low temperature suggests a full energy gap. At high temperature above the transition, a small amount of itinerant carriers with short life time x is observed, which is gapped at 20 K with a direct gap of 0.24 eV. Our first-principles calculations indicate that the antiferromagnetic (AFM) correlation with intermediate Coulomb repulsion U could effectively split Os(4b>) t_(2g) bands and push them away from Fermi level (E_F). On the other hand, a noncollinear magnetic interaction is needed to push the Os(4c) bands away from Ep, which could be induced by Os(4c)-Os(4c) frustration. Therefore, AFM correlation, Coulomb repulsion U and noncollinear interaction all play important roles for the insulating ground state in Ca_2Os_2O_7.
机译：我们介绍了Weberite结构Ca_2O_s2O_7单晶/多晶样品的比热，磁化强度，光谱学测量和第一性原理计算。 Ca_2O_s2O_7在高温下表现出居里-魏斯性质，并且在冷却时以327 K进入亚铁磁绝缘状态。在比热中的327 K处观察到一个类似X的峰，这意味着一个二级相变。低温下电子比热的消失表明整个能隙。在跃迁以上的高温下，观察到少量的具有短寿命x的流动性载流子，其在20 K时有间隙，直接间隙为0.24 eV。我们的第一性原理计算表明，与中间库仑排斥U的反铁磁（AFM）相关性可以有效地分裂Os（4b>）t_（2g）波段，并将其推离费米能级（E_F）。另一方面，需要非共线磁性相互作用来将Os（4c）带推离Ep，这可能是由Os（4c）-Os（4c）挫败感引起的。因此，AFM相关，库仑排斥U和非共线相互作用都对Ca_2Os_2O_7中的绝缘基态起着重要作用。

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  • 来源
    《Physical review》 |2012年第19期|195108.1-195108.7|共7页
  • 作者

    P. Zheng; Y. G. Shi; Q. S. Wu; G. Xu; T. Dong; Z. G. Chen; R. H. Yuan; B. Cheng; K. Yamaura; J. L. Luo; N. L. Wang;

  • 作者单位

    Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People's Republic of China;

    Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People's Republic of China;

    Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People's Republic of China;

    Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People's Republic of China;

    Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People's Republic of China;

    Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People's Republic of China;

    Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People's Republic of China;

    Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People's Republic of China;

    Superconducting Properties Unit, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044 Ibaraki, Japan;

    Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People's Republic of China;

    Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People's Republic of China;

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  • 关键词

    metal-insulator transitions and other electronic transitions; transition-metal compounds; infrared and raman spectra;

    机译：金属-绝缘体过渡和其他电子过渡;过渡金属化合物;红外光谱和拉曼光谱;

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