LaFeAsO中的相变：结构、磁性、弹性和输运性质，heat capacity和穆斯堡尔谱
Phase transitions in LaFeAsO: structural, magnetic, elastic, and transport properties, heat capacity and Mossbauer spectra
摘要：
我们目前的结果从一个详细的实验研究的LaFeAsO，在一系列的“FeAs”为基础的oxypnictide超导体的母体材料。冷却后，该材料在~160 K经历四方-正交晶体相变，紧接着在145 K附近发生反铁磁有序化。这些相变使用温度相关的粉末X射线和中子衍射测量的分析。由低温相的穆斯堡尔谱导出了~0.35玻尔磁子/铁的磁矩。在远高于衍射数据中的结构转变（高达近200 K）的温度下观察到的结构转变的证据，以及通过共振超声光谱测量探测的多晶弹性模量。这两个相变对LaFeAsO的输运性质（电阻率、热导率、Seebeck系数、Hall系数）、热容和磁化强度的影响也被报道，包括在低于160 K时Hall系数的幅度的急剧增加。结果表明，结构畸变导致的本地化的Fe上的载流子，产生小的局部磁矩，随后反铁磁顺序进一步冷却。还观察到在高温四方相中存在强的电子-声子相互作用的证据。
英文摘要：
We present results from a detailed experimental investigation of LaFeAsO, the parent material in the series of "FeAs" based oxypnictide superconductors. Upon cooling this material undergoes a tetragonal-orthorhombic crystallographic phase transition at ~160 K followed closely by an antiferromagnetic ordering near 145 K. Analysis of these phase transitions using temperature dependent powder X-ray and neutron diffraction measurements is presented. A magnetic moment of ~0.35 Bohr magnetons per iron is derived from Mossbauer spectra in the low temperature phase. Evidence of the structural transition is observed at temperatures well above the structural transition (up to near 200 K) in the diffraction data as well as the polycrystalline elastic moduli probed by resonant ultrasound spectroscopy measurements. The effects of the two phase transitions on the transport properties (resistivity, thermal conductivity, Seebeck coefficient, Hall coefficient), heat capacity, and magnetization of LaFeAsO are also reported, including a dramatic increase in the magnitude of the Hall coefficient below 160 K. The results suggest that the structural distortion leads to a localization of carriers on Fe, producing small local magnetic moments which subsequently order antiferromagnetically upon further cooling. Evidence of strong electron-phonon interactions in the high-temperature tetragonal phase is also observed.
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