CRYSTAL-FIELD EFFECTS IN THE ELECTRON-SPIN-RESONANCE OF GD3+ AND ER3+ IN PR2CUO4

The low-temperature (T < 300 K) electron-spin-resonance (ESR) spectra of Gd3+ and Er3+ in Pr2CuO4 show symmetry properties appropriate to the crystal tetragonal symmetry. The completely resolved Gd3+ spectra allowed us to measure, at T = 2 K, the principal g values g parallel-to = 1.985(8), g perpendicular-to =2.040(8), and the crystal-field parameters [b2(0) = -399(2) X 10(-4) cm-1, b4(0) = -33.1(7) X 10(-4) cm-1, and b4(4) = 205(3) X 10(-4) cm-1]. The large broadening of the ESR lines, observed above T approximately 40 K, is due to a relaxation via the thermally populated crystal-field excited Pr levels. For Er3+ in Pr2CuO4 we observe a single ESR line corresponding to a ground-state doublet with g parallel-to = 17.94(5) and g perpendicular-to less-than-or-equal-to 0.2. The absence of any splittings of the ESR lines below the Neel temperature implies that the magnetostatic dipole field at the rare-earth-ion site due to the antiferromagnetically ordered Cu moments is < 45 Oe.