新型钙钛矿铜氧材料Sr_8 CaRe_3 Cu_4 O_(24)的亚铁磁和轨道有序性质

Orbital order and ferrimagnetic properties of the new compound Sr_8 CaRe_3 Cu_4 O_(24)

用密度泛函理论和格林函数方法研究了新型钙钛矿铜氧材料Sr8CaRe3Cu4O24的电子结构和磁性性质.所得结果与实验符合得很好,表明这种材料是绝缘体,每个元胞有1.0μB的磁矩.磁矩主要在Cu原子上,相邻Cu原子上的磁矩反平行排列.非磁的Re原子使得Cu上的d轨道有序排列,这导致这种材料有很高的居里温度(TC≈440K).基于密度泛函的结果,用海森伯模型描述了材料的电子自旋自由度,并用格林函数方法研究了材料有限温度下的磁性行为,所得结果和实验一致,表明自旋为1和自旋为1/2磁矩交错排列的海森伯模型可很好地描述这种材料的磁性性质.

We investigate the electronic and magnetic properties of the new compound Sr8CaRe3Cu4O24 by means of density functional theory and the Green function method. Our density functional calculation shows that this system is an insulator with a net magnetic moment of 1.0μ8/f.u. , which is in good agreement with experiment. The magnetic moments are mainly located at Cu atoms, and at neighboring Cu sites they are aligned antiparallel to one another. It is the non-magnetic Re atoms that induce orbital ordering of the d electrons in the Cu atoms, which is responsible for the strong exchange interaction and the high magnetic transition temperature. Based on these results we introduce an effective model for the spin degrees of freedom, and investigate the finite-temperature properties by the Green function method. The results obtained are consistent with the experimental results, indicating that the spin-alternating Heisenberg model is suitable for this compound.