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首页> 外文期刊>Physical review >Observation of a phase transition at 55 K in single-crystal CaCu_(1.7)As_2
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Observation of a phase transition at 55 K in single-crystal CaCu_(1.7)As_2

机译：CaCu_（1.7）As_2单晶中55 K时的相变观察

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We present the structural, magnetic, thermal and ab-plane electronic transport properties of single crystals of CaCu_(1.7)As_2 grown by the self-flux technique that were investigated by powder x-ray diffraction, magnetic susceptibility x, isothermal magnetization M, specific heat C_p, and electrical resistivity p measurements as a function of temperature T and magnetic field H. X-ray diffraction analysis of crushed crystals at room temperature confirm the collapsed tetragonal ThCr_2Si_2-type structure with -15% vacancies on the Cu sites as previously reported, corresponding to the composition CaCu_(1.7)As_2. The x(T) data are diamagnetic, anisotropic, and nearly independent of T. The x is larger in the ab plane than along the c axis, as also observed previously for SrCu_2 As_2 and for pure and doped BaFe_2As_2. The C_P(T) and p(T) data indicate metallic sp-band character. In contrast to the x(T) and C_p(T) data that do not show any evidence for phase transitions below 300 K, the p(T) data exhibit a sharp decrease on cooling below a temperature T_t = 54-56 K, depending on the crystal. The p(T) data show no hysteresis on warming and cooling through T_t and the transition thus appears to be second order. The phase transition may arise from spatial ordering of the vacancies on the Cu sublattice. The T_t is found to be independent of H for H ≤ 8 T. A positive magnetoresistance is observed below T_t that increases with decreasing T and attains a value in H = 8.0 T of 8.7% at T = 1.8 K.
机译：通过粉末X射线衍射，磁化率x，等温磁化强度M，比重，自磁通量技术研究了通过自磁通技术生长的CaCu_（1.7）As_2单晶的结构，磁，热和ab平面电子传输性质。热量C_p和电阻率p测量值与温度T和磁场H的关系。室温下破碎晶体的X射线衍射分析证实，崩溃的四方ThCr_2Si_2型结构在Cu位点上的空位为-15％，如先前报道，对应于成分CaCu_（1.7）As_2。 x（T）数据是反磁性的，各向异性的，并且几乎与T无关。如先前在SrCu_2As_2和纯掺杂BaFe_2As_2中观察到的，x在ab平面中大于沿c轴。 C_P（T）和p（T）数据表示金属sp带特征。与x（T）和C_p（T）数据没有显示任何证据表明低于300 K的相变相反，p（T）数据在冷却至温度T_t = 54-56 K以下时会急剧下降，具体取决于在水晶上。 p（T）数据显示在通过T_t的加热和冷却过程中没有滞后现象，因此转变似乎是二阶的。相变可能是由于Cu亚晶格上空位的空间顺序而引起的。对于H≤8 T，发现T_t与H无关。在T_t以下观察到正磁阻，该磁阻随T的减小而增加，并且在T = 1.8 K时，H = 8.0 T的值为8.7％。

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