A microscopic theory was presented for the spin-Hamiltonian parameters of 6S(d5) ions of trigonal symmetry. This established the relationship between the spin-Hamiltonian and crystal-field parameters. It permitted the study of the net-charge compensation spin-Hamiltonian effect which resulted from the net-charge compensation crystal-field contribution of Fe3+ ions at trigonal K+ vacancy sites in Fe3+-doped KZnF3. Microscopic contributions to the net-charge compensation crystal-field parameters were then investigated by proposing a vacancy-induced lattice distortion model that was based upon electron nuclear double resonance data. In particular, the vacancy-induced and distortion-induced dipole effects were considered and the former was found to be important.

W.Yu: Physical Review B, 1995, 52[6], 4237-44