Investigations of the spin hamiltonian parameters and local structure for Cr$^{3+}$ in K$_2$PdCl$_4$ single crystal

Abstract

The spin Hamiltonian parameters (SHPs) (g factors and zero-field splittings (ZFSs) D and E) and the local structure for Cr$^{3+}$ in K$_2$PdCl$_4$ single crystal are theoretically investigated from the perturbation calculations of the SHPs for an orthorhombically distorted octahedral 3d$^3$ cluster. The impurity Cr$^{3+}$ is found not to occupy the conventional square planar Pd$^{2+}$ site but to locate at the octahedral K$^{+}$ site, associated with the relative axial compression ratio $ \rho $($ \approx $ 11.1%) and the perpendicular bond length variation ratio $ \tau $($ \approx $ 11.7%). The impurity centre exhibits much smaller axial compression distortion and much larger perpendicular orthorhombic distortion than the host K$^+$ site in K$_2$PdCl$_4$ ($\rho_H \approx 18.6$% and $\tau_H \approx 0$) and hence a more regular ligand octahedron, corresponding to the very small ZFSs. The contributions to $g$-shifts $ \Delta g_{\textrm{CT}} $ from the CT mechanism are opposite in sign and twenty-one times larger in magnitude compared with $ \Delta g_{\textrm{CF}} $ from the CF mechanism. For the ZFSs, the CT contributions D$_{\textrm{CT}}$ and E$_{\textrm{CT}}$ are opposite in sign and almost the same in magnitude with respect to the corresponding D$_{\textrm{CF}}$ and E$_{\textrm{CF}}$.