ESR ofGd3+andEr3+inPr2−xCexCuO4

Abstract

Electron spin resonance (ESR) of ${\mathrm{Gd}}^{3+}$ and ${\mathrm{Er}}^{3+}$ in single crystals of ${\mathrm{Pr}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ce}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ (0≤x≤0.15) at liquid-helium temperature shows crystal field (CF) effects corresponding to a ${\mathit{C}}_{4\mathit{v}}$ point symmetry. Upon doping with ${\mathrm{Ce}}^{4+}$, a reduction of about 23% in the second-order CF parameter ‖${\mathit{b}}_{20}$‖ is found with no significant change for the other CF spin-Hamiltonian parameters. The resonance lines broaden and present a Dysonian line shape at higher ${\mathrm{Ce}}^{4+}$ concentration, which is consistent with an increase in the CF inhomogeneity and the metallic character of the compound. Magnetic-susceptibility measurements present a small increase in the low-temperature anisotropy upon doping, consistent with a smaller 〈‖${\mathit{B}}_0^2$‖〉 crystal-field parameter for ${\mathrm{Pr}}^{3+}$ in ${\mathrm{Pr}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ce}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$. The reduction in the CF parameters is tentatively attributed to charge transfer from Ce atoms to the ${\mathrm{CuO}}_2$ planes. The exchange parameters ${\mathit{j}}_{\mathrm{Gd}\mathrm{-}\mathrm{Pr}}$ and ${\mathit{j}}_{\mathrm{Pr}\mathrm{-}\mathrm{Pr}}$ are estimated from the ESR and susceptibility measurements.