THE ROLE OF VACANCIES IN THE MAGNETIC AND MAGNETOOPTIC PROPERTIES OF TB-DOPED EUO AND EUS FILMS

Rocksalt structure solid solutions were prepared by coevaporating Eu2O 3 and Th metal. The films have the general formula Eu1-xTbxO1-ysquarey where y, the oxygen vacancy fraction, is given by y=(3x-1)/2. We have also prepared Tb-doped EuS solid solutions where y congruent-to x so we can compare the effects of anion vacancies in both the oxide and su lfide systems. The coercivity, H(c), increases rapidly with Th doping at about x=0.15 in the sulfide system and x=0.45 in the oxide system. The H(c) of both systems falls on a universal curve, however, when plo tted vs vacancies/RE (square/RE) with the rapid increase occurring at square/RE=0.15. This value is close to 1/6 (0.166) which in octahedral coordination corresponds to one anion vacancy/RE. This suggests that the near neighbor vacancy is producing a strong crystal field at the T h site which causes strong single ion anisotropy and thus a high coerc ivity. The MO spectra of the oxides show a strong dependence on x. At x=0. 25, peaks are observed at 1.5 eV (-3-degrees), 2.2 eV (5.5-degree s), and 2.7 eV (-2-degrees). At x=0.33, the spectra change completely. A narrow peak with a rotation theta(K)=-20-degrees appears at 2.5 eV, dominating the spectrum. The reflectivity, R, goes through a sharp mi nimum at the same energy (R < 1 %), possibly causing the enhancement i n theta(K).