Paramagnetic Resonance of Er 3+ and Dy 3+ in Natural Single Crystals of Zircon

The paramagnetic resonance of two rare‐earth ions Er 3+ and Dy 3+ , not previously reported in the literature, was observed in natural single crystals of zircon. The spectra were observed at 4.2 °K at 9 and 35 GHz. For both ions well‐resolved hyperfine structure was observed corresponding to the natural isotopic abundances of both ions. In particular for Er 3+ in the perpendicular direction forbidden Δ m = ±2 lines were observed, from which an accurate value of P was calculated. The spectra were fitted by a spin‐Hamiltonian containing electronic Zeeman, hyperfine, and nuclear quadrupole terms for Er 3+ and electronic Zeeman and hyperfine terms for Dy 3+ .