Paramagnetic Resonance of Trivalent Holmium Ions in Calcium Tungstate

Paramagnetic resonance has been observed in calcium tungstate containing trivalent holmium ions in sites with tetragonal symmetry. The observed spectrum was fitted to the spin Hamiltonian H=g_∥βHcosθSZ+ΔₓSₓ+ΔySy+ASzIz with $A=0.299$ cm^-1 and g_∥=13.691. The distortion parameter Δ=(Δₓ^_²+Δy^_²)1/2 did not possess a unique value and consequently the absorption line shape was asymmetric, the value of Δ corresponding to the peak intensity being 0.03 cm^-1. These results for Ho³⁺ are contrasted with those published for Tb³⁺ in CaWO₄ and attention is drawn to the differences in line shape in the two cases. It is found that the lowest level in CaWO₄/Ho³⁺ is of the type Ψ=φ|±7〉+χ|±3〉+ψ|∓1〉+Ω|∓5〉 Finally, the results of paramagnetic-resonance measurements on all trivalent rare-earth ions in tetragonal sites in CaWO₄ are summarized in an Appendix.