掺杂晶体材料ZnGa2O4：Fe3+局域结构畸变及其微观自旋哈密顿参量研究

摘要

基于Newman的晶场叠模型与微观自旋哈密顿理论,建立了ZnGa2O4：Fe3+晶体材料中磁性离子Fe3+局域结构与其自旋哈密顿(spin-Hamiltonian, SH)参量(包括二阶零场分裂(zero-field splitting, ZFS)参量D,四阶ZFS参量(a-F ), Zeeman g因子： g//, g⊥,∆g(= g//-g⊥))之间的定量关系.采用以全组态完全对角化方法为理论背景的CFA/MSH(Crystal Filed Analysis/Microscopic Spin Hamiltonian)研究软件,研究了ZnGa2O4：Fe3+材料中磁性离子Fe3+的SH参量与其局域结构的依赖关系.研究表明：对于ZnGa2O4：Fe3+晶体材料,当磁性离子Fe3+的局域结构畸变参数∆R =0.0487 nm,∆θ=0.192◦时,其基态SH参量理论计算结果与实验测量符合很好,进一步表明Fe3+掺入晶体材料后将引起磁性Fe3+离子局域结构的微小畸变,但其仍然保持D3d点群对称局域结构.在此基础上研究分析了SH参量的微观起源,结果表明：ZnGa2 O4：Fe3+晶体材料的SH参量主要来源于SO(spin-orbit)磁相互作用机理,来自其他磁相互作用机理(包括SS(spin-spin), SOO(spin-other-orbit), OO(orbit-orbit), SO-SS-SOO-OO)的贡献比较小.%Relations between the spin-Hamiltonian (SH) parameters including the second-order zero-field splitting (ZFS) pa-rameter D,the fourth-order ZFS parameter (a-F ), the Zeeman g-factors: g//, g⊥, ∆g(= g//-g⊥) and the structural parameters of ZnGa2O4:Fe3+ crystals have been established by means of the microscopic spin Hamiltonian theory and Newman’s crystal field (CF) superposition model. On the basis of this, the SH parameters for Fe3+ magnetic ions in ZnGa2O4:Fe3+ crystals are investigated theoretically using the CFA/MSH (crystal field analysis/microscopic spin-Hamiltonian) software based on the full configuration complete diagonalization method. It is found that the theoretically calculated parameters including the ZFS parameters D, (a-F ), and the Zeeman g-factors: g//, g⊥, ∆g(=g//-g⊥) for ZnGa2O4:Fe3+ crystals are in good agreement with experimental data when taking into account the lattice distortions:∆R = 0.0487 nm and ∆θ = 0.192◦. This investigation reveals that there is a slight local structure distortion due to Fe3+ ions in ZnGa2O4:Fe3+ crystals, but the site of Fe3+ still retains D3d symmetry. On the other hand, it is found for Fe3+ ions in ZnGa2O4:Fe3+ crystals that the contribution to the SH parameters from the spin-orbit (SO) mechanism is the most important one, whereas the contributions to the SH parameters from other four mechanisms, including the spin-spin (SS), spin-other-orbit (SOO), orbit-orbit (OO), and SO-SS-SOO-OO mechanisms, are small.