BaCo2As2、Ba{0.94}K{0.06} Co2As2和Ba{0.78}K{0.22} Co2As2的晶体结构和物理性质
Crystallography and Physical Properties of BaCo2As2, Ba{0.94}K{0.06}Co2As2 and Ba{0.78}K{0.22}Co2As2
摘要：
用X射线衍射、中子粉末衍射、磁化率、磁化强度、热容Cp、{75}As NMR和电阻率ρ随温度T的变化研究了BaCo_2As_2和掺K的Ba{1-x}K{x} Co_2As_2（x = 0.06，0.22）多晶和单晶样品的晶体学和物理性质。使用Sn助熔剂和CoAs自助熔剂生长晶体，其中Sn生长的晶体含有1.6-2.0摩尔%的Sn。所有样品均为四方ThCr_2Si_2型结构（空间群I_4/mmm）。对于BaCo 2As 2，粉末中子衍射数据表明，c轴晶格参数表现出反常的负热膨胀从10到300 K，而a轴晶格参数和晶胞体积显示正常的正热膨胀在这个T范围内。在BaCo 2As 2中没有发现从任何测量的T范围内的过渡。在40-50 K以下，我们发现rho ~ T^2指示费米液体的基态。在费米能级D（EF）~ 18态/（eV f. u.）从低T Cp（T）测量中发现了两个自旋方向的电子态密度，而能带结构计算给出D（EF）= 8.23态/（eV f.u.）。{75}As NMR位移数据与T的关系与chi（T）数据具有相同的T依赖性，表明导出的chi（T）数据是内在的。所观察到的{75}As核自旋动力学与铁磁和/或条纹型反铁磁自旋涨落的存在是一致的。Ba{0.78}K{0.22} Co_2As_2晶体在Sn助熔剂中生长，其性质与未掺杂的BaCo_2As_2非常相似。另一方面，从两批的Ba{0.94}K{0.06} Co2 As 2生长在CoAs自熔剂中的晶体在T < 10 K时显示出弱铁磁性的证据，在1.8 K时具有小的有序矩，分别为0.007和0.03 μ B/分子式单位。
英文摘要：
The crystallographic and physical properties of polycrystalline and single crystal samples of BaCo2As2 and K-doped Ba{1-x}K{x}Co2As2 (x = 0.06, 0.22) are investigated by x-ray and neutron powder diffraction, magnetic susceptibility chi, magnetization, heat capacity Cp, {75}As NMR and electrical resistivity rho measurements versus temperature T. The crystals were grown using both Sn flux and CoAs self-flux, where the Sn-grown crystals contain 1.6-2.0 mol% Sn. All samples crystallize in the tetragonal ThCr2Si2-type structure (space group I4/mmm). For BaCo2As2, powder neutron diffraction data show that the c-axis lattice parameter exhibits anomalous negative thermal expansion from 10 to 300 K, whereas the a-axis lattice parameter and the unit cell volume show normal positive thermal expansion over this T range. No transitions in BaCo2As2 were found in this T range from any of the measurements. Below 40-50 K, we find rho ~ T^2 indicating a Fermi liquid ground state. A large density of states at the Fermi energy D(EF) ~ 18 states/(eV f.u.) for both spin directions is found from low-T Cp(T) measurements, whereas the band structure calculations give D(EF) = 8.23 states/(eV f.u.). The {75}As NMR shift data versus T have the same T dependence as the chi(T) data, demonstrating that the derived chi(T) data are intrinsic. The observed {75}As nuclear spin dynamics are consistent with the presence of ferromagnetic and/or stripe-type antiferromagnetic spin fluctuations. The crystals of Ba{0.78}K{0.22}Co2As2 were grown in Sn flux and show properties very similar to those of undoped BaCo2As2. On the other hand, the crystals from two batches of Ba{0.94}K{0.06}Co2As2 grown in CoAs self-flux show evidence of weak ferromagnetism at T < 10 K with small ordered moments at 1.8 K of 0.007 and 0.03 muB per formula unit, respectively.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
