Electron spin resonance of axially symmetruc Cr3+ centres in KMgF3 and KZnF3

The ESR spectra of five Cr3+ centres in KMgF3 and KZnF3 are reported. All are axially symmetric and can be described by the spin-Hamiltonian H = gsub(parallel to)βBsub(z) Ssub(z) + gsub(perpendicular to) β(Bsub(x)Ssub(x) + Bsub(y)Ssub(y)) + D [Ssub(z)sup(2) - 1/3S(S + 1)] with S = 3/2. In KMgF3 one finds spectra with D = -0.1528 cm-1 (trigonal), D =-0.2167 cm-1 (tetragonal) and D = -2.4 cm-1 (tetragonal). In KZnF3, centres are found with D = -0.1613 cm-1 (trigonal) and D = -0.0522 cm-1 (tetragonal). The trigonal spectra are ascribed to Cr3+ ions associated with K+ vacancies. The tetragonal spectra are attributed to Cr3+ ions with divalent cation vacancies, with O2- ions or with other impurities on the tetragonal axis. (author)