Crystal-field effects in the electron-spin resonance ofGd3+andEr3+inPr2CuO4

Abstract

The low-temperature (T${\mathrm{Gd}}^{3+}$ and ${\mathrm{Er}}^{3+}$ in ${\mathrm{Pr}}_2$ ${\mathrm{CuO}}_4$ show symmetry properties appropriate to the crystal tetragonal symmetry. The completely resolved ${\mathrm{Gd}}^{3+}$ spectra allowed us to measure, at T=2 K, the principal g values ${\mathit{g}}_{\mathrm{?}}$=1.985(8), ${\mathit{g}}_{\mathrm{\perp }}$=2.040(8), and the crystal-field parameters [${\mathit{b}}_2^0$=-399(2)×${10}^{\mathrm{-}4}$ ${\mathrm{cm}}^{\mathrm{-}1}$, ${\mathit{b}}_4^0$=-33.1(7)×${10}^{\mathrm{-}4}$ ${\mathrm{cm}}^{\mathrm{-}1}$, and ${\mathit{b}}_4^4$=205(3)×${10}^{\mathrm{-}4}$ ${\mathrm{cm}}^{\mathrm{-}1}$]. The large broadening of the ESR lines, observed above T∼40 K, is due to a relaxation via the thermally populated crystal-field excited Pr levels. For ${\mathrm{Er}}^{3+}$ in ${\mathrm{Pr}}_2$ ${\mathrm{CuO}}_4$ we observe a single ESR line corresponding to a ground-state doublet with ${\mathit{g}}_{\mathrm{?}}$=17.94(5) and ${\mathit{g}}_{\mathrm{\perp }}$≤0.2. The absence of any splittings of the ESR lines below the Néel temperature implies that the magnetostatic dipole field at the rare-earth-ion site due to the antiferromagnetically ordered Cu moments is