Mahnetic and Electric Properties of Double Perovskites containing Rare-earth and Platinum Elements

研究了双钙钛矿Ca_2LnRuO_6 （Ln = Y, La-Lu）的磁性能。从磁化率和比热测量中发现，所有这些化合物都表现出反铁磁跃迁（T_N = 10-34K），并且Ru^<+5 b>离子的反铁磁有序发生在这些温度以下。在这些化合物中，较大的Ln离子倾向于占据ABO_3钙钛矿的A位，而较小的Ln离子倾向于占据B位。Ca_2NdRuO_6中的Nd离子位于A位，在1.6 K时发生反铁磁跃迁，远低于T_N = 11.5 K。另一方面，Ca_2YbRuO_6中的Yb离子位于B位，并且由于Yb^<3+>和Ru^<5+>离子的存在，在34 K时发生了远程反铁磁有序。采用粉末中子衍射法测定了Ca_2YbRuO_6的磁性结构。此外，用粉末x射线衍射Rietveld法测定了三元钾稀土氧化物KLnO_2 （Ln = Y, Nd, Sm-Lu）。所有的KLnO_2化合物都具有相同的六方a-NaFeO_2结构。这些化合物的磁化率测量表明，顺磁性行为低至1.8 K。比热测量结果表明，Gd、Dy、Ho和Er化合物分别在1.1、1.8、1.2和0.8 K处存在磁异常。

Magnetic properties of double perovskites Ca_2LnRuO_6 (Ln = Y, La-Lu) were investigated. From the magnetic susceptibility and specific heat measurements, it is found that all these compounds show an antiferromagnetic transition (T_N = 10-34K), and that the antiferromagnetic ordering of Ru^<+5> ions occurs below these temperatures. In these compounds, the larger Ln ions tend to occupy the A site of the perovskite ABO_3, while the smaller Ln ions tend to occupy the B site. The Nd ions in Ca_2NdRuO_6 are situated at the A site and show an antiferromagnetic transition at 1.6 K, which is much lower than T_N = 11.5 K. On the other hand, the Yb ions in Ca_2YbRuO_6 are situated at the B site, and a long-range antiferromagnetic ordering due to both Yb^<3+> and Ru^<5+> ions occurs at 34 K. The magnetic structure of Ca_2YbRuO_6 was determined by powder neutron diffraction measurements.In addition, ternary potassium rare earth oxides KLnO_2 (Ln = Y, Nd, Sm-Lu) have been determined by powder X-ray diffraction using the Rietveld analysis method. All of the KLnO_2 compounds have the same hexagonal a-NaFeO_2 structure. Magnetic susceptibility measurements for these compounds show paramagnetic behavior down to 1.8 K. The specific heat measurements indicate that the Gd, Dy, Ho and Er compounds have a magnetic anomaly at 1.1, 1.8, 1.2 and 0.8 K, respectively.