Saito Takashi, Yamada Ryuta, Ritter Clemens, Senn Mark S, Attfield J Paul, Shimakawa Yuichi
Institute for Chemical Research, Kyoto University , Gokasho, Uji, Kyoto 611-0011, Japan.
Inorg Chem. 2014 Feb 3;53(3):1578-84. doi: 10.1021/ic402616r. Epub 2014 Jan 21.
A-site-ordered perovskite Ce1/2Cu3Ti4O12 has been found to crystallize in two different forms, one with random and the other with ordered Ce/vacancy distribution at the A site of the prototype AA'3B4O12 structure. The random phase is isostructural with CaCu3Ti4O12, and the ordered phase is a new ordered derivative of the AA'3B4O12-type perovskite with two crystallographically distinct Cu sites. Although both phases form a G-type antiferromagnetic arrangement of Cu(2+) spins below 24 K, their magnetisms are quite different. A typical antiferromagnetic transition is observed in the random phase, whereas a small ferromagnetic moment appears below 24 K in the ordered phase, which rapidly decreases upon further cooling. A mean-field approximation approach revealed that this unusual behavior in the ordered phase is an L-type ferrimagnetism driven by the nonequivalent magnetizations of the two ferromagnetic Cu(2+) spin sublattices in the G-type spin structure. This unusual ferrimagnetism is a direct consequence of the Ce/vacancy ordering.
A位有序的钙钛矿Ce1/2Cu3Ti4O12已被发现以两种不同形式结晶，一种在原型AA'3B4O12结构的A位具有随机的Ce/空位分布，另一种具有有序的Ce/空位分布。随机相与CaCu3Ti4O12同构，有序相是具有两个晶体学上不同Cu位点的AA'3B4O12型钙钛矿的新有序衍生物。尽管两个相在24 K以下都形成了Cu(2+)自旋的G型反铁磁排列，但它们的磁性有很大不同。在随机相中观察到典型的反铁磁转变，而在有序相中，在24 K以下出现小的铁磁矩，进一步冷却时该铁磁矩迅速减小。平均场近似方法表明，有序相中的这种异常行为是由G型自旋结构中两个铁磁Cu(2+)自旋子晶格的不等价磁化驱动的L型亚铁磁性。这种异常的亚铁磁性是Ce/空位有序化的直接结果。
