Materials Department, University of California, Santa Barbara, CA 93106, USA.
J Phys Condens Matter. 2012 Feb 1;24(4):046003. doi: 10.1088/0953-8984/24/4/046003.
We examine the evolution of magnetic properties in the normal spinel oxides Mg(1-x)Cu(x)Cr2O4 using magnetization and heat capacity measurements. The end-member compounds of the solid solution series have been studied in some detail because of their very interesting magnetic behavior. MgCr2O4 is a highly frustrated system that undergoes a first-order structural transition at its antiferromagnetic ordering temperature. CuCr2O4 is tetragonal at room temperature as a result of Jahn-Teller active tetrahedral Cu2+ and undergoes a magnetic transition at 135 K. Substitution of magnetic cations for diamagnetic Mg2+ on the tetrahedral A site in the compositional series Mg(1-x)Cu(x)Cr2O4 dramatically affects magnetic behavior. In the composition range 0 ≤ x ≤ ≈0.3, the compounds are antiferromagnetic. A sharp peak observed at 12.5 K in the heat capacity of MgCr2O4 corresponding to a magnetically driven first-order structural transition is suppressed even for small x. Uncompensated magnetism--with open magnetization loops--develops for samples in the x range ≈0.43 ≤ x ≤ 1. Multiple magnetic ordering temperatures and large coercive fields emerge in the intermediate composition range 0.43 ≤ x ≤ 0.47. The Néel temperature increases with increasing x across the series while the value of the Curie-Weiss Θ(CW) decreases. A magnetic temperature-composition phase diagram of the solid solution series is presented.
我们使用磁化和热容测量研究了正常尖晶石氧化物 Mg(1-x)Cu(x)Cr2O4 中磁性的演变。由于其非常有趣的磁行为，固溶系列的端元化合物已被进行了详细研究。MgCr2O4 是一个高度受挫的系统，在其反铁磁有序温度下经历一级结构相变。CuCr2O4 在室温下为四方晶系，由于 Jahn-Teller 活性四面体 Cu2+，在 135 K 时发生磁转变。在 Mg(1-x)Cu(x)Cr2O4 组成系列中，用磁性阳离子取代非磁性 Mg2+ 占据四面体 A 位，这极大地影响了磁行为。在 0 ≤ x ≤ ≈0.3 的组成范围内，化合物呈反铁磁性。MgCr2O4 热容中在 12.5 K 处观察到的对应于磁驱动一级结构相变的尖锐峰被抑制，即使对于小 x 也是如此。在 x 范围 ≈0.43 ≤ x ≤ 1 的样品中，出现未补偿的磁（具有开磁化回路）。在中间组成范围内 0.43 ≤ x ≤ 0.47 出现多个磁有序温度和大矫顽场。在整个系列中，随着 x 的增加，奈尔温度增加，而居里-外斯 Θ(CW)的值减小。提出了固溶系列的磁温度组成相图。
