Magnetic Excitations of Mixed CoF2/ZnF2 Crystals

The magnetic excitations in mixed crystals of Co1-cZncF2 with c=0.14+or-0.02, 0.31+or-0.03 and 0.77+or-0.10 have been measured using neutron inelastic scattering techniques. The results for the first two crystals show that the excitations decrease in frequency with increasing zinc concentration and also have a finite lifetime.

For the crystal containing the largest concentration of ZnF2 well defined magnetic excitations were not observed. These results are very similar to the predictions of the virtual lattice model in which each exchange interaction of CoF2 is reduced by the concentration of CoF2 in the mixed crystal. Reasonable agreement is also found with the results of calculations based on the single-site CPA approximation but the results do not clearly show that any one of the particular variants of this model gives a markedly better result than any of the other variants.