EPR investigations of the superhyperfine interaction and of the zero-field splittings for cubic and tetragonal Gd3+centres at sixfold coordinated sites in AMF3crystals

Abstract

In RbCaF3, CsCaF3, and RbCdF3 crystals the 8S Gd3+ ion is substituted for the sixfold coordinated Ca2+ or Cd2+ ions. The authors discuss the superhyperfine interaction with the ligands and the hexadecapolar crystal-field term for cubic centres. Tetragonal centres, in which the quadrupolar crystal field terms range from 1.5*10-4 to 0.3 cm-1, were obtained through uniaxial stress, a structural phase change below Tc, or charge compensation by vacancies and O2- impurities. The authors discuss this term by using theoretical results within an ionic model or an empirical superposition model proposed by Newman (1975).