稀土掺杂对钴铁氧体电子结构和磁性能影响的理论研究

尖晶石型铁氧体是十分重要的磁性材料之一, 具有独特的物理性质、化学特性、磁学特性和电子特性. 其中尖晶石型钴铁氧体具有较好的电磁性质而被广泛应用. 本文基于密度泛函理论(DFT) 的第一性原理平面波赝势法, 结合广义梯度近似(GGA+U), 研究了CoRE_0.125Fe_1.875O₄ (RE = Nd, Eu, Gd)体系的电子结构和磁性能. 结果表明随着稀土元素从Nd到Gd掺杂体系晶胞的晶格常数呈递减趋势. 磁性能依赖于稀土离子(RE³⁺)4f轨道未配对的电子数, 掺杂Eu和Gd能够提高钴铁氧体体系的磁矩, 主要因为它们3+价态离子具有较多未配对的4f电子, 因而对磁性能的影响较大. 然而Nd 的掺杂对体系磁性能的影响很小, 这是由于它的离子半径较大, 导致晶格发生畸变.

Theoretical study on the influence of rare earth doping on the electronic structure and magnetic prop erties of cobalt ferrite

Spinel ferrite is one of the very important magnetic materials, having the unique physical properties, chemical properties, magnetic properties, and electronic properties. CoFe₂O₄ is widely used due to their good electromagnetic properties. We have studied the electronic structure and magnetic properties of CoRE_0.125Fe_1.875O₄ (RE = Nd, Eu, Gd)by first-principles plane-wave pseudopotential method based on density functional theory (DFT), combined with the generalized gradient approximation (GGA + U) in this paper. Results show that the lattice constants of the compunds CoFe_1.875RE_0.125O₄ (RE=Nd, Eu and Gd) will decrease due to the decreasing ionic radius of RE as the atomic number increases. Their magnetic properties depend on the unpaired 4f electrons of RE³⁺ ions, and the net magnetic moment of CoFe₂O₄ will increase with Eu and Gd doping, mainly because there are more unpaired 4f electrons in Eu³⁺ and Gd³⁺. Thus the doping of Eu³⁺ and Gd³⁺ may have a greater impact on the magnetic properties of cobalt ferrite. The contribution from the doping of Nd is not remarkable on the magnetic properties, since the Nd^{3 +} ion, having a larger ionic radius, could distort the crystal structure of CoFe₂O₄.