Influence of nitrogen, oxygen, and water on magnetic properties of dc magnetron sputtered GdTbFe films

Abstract

Amorphous GdTbFe thin films were produced by dc magnetron sputtering in argon atmosphere at varying partial pressures of nitrogen, oxygen, and water. The compensation temperature Tcomp, the Curie temperature TC, and the uniaxial magnetic anisotropy constant Ku decrease strongly with increasing impurity concentration in the films. The influence of nitrogen on Tcomp and Ku is about a factor of 3 less than that of oxygen and water. The strong decrease of Tcomp and Ku is due to the preferred reaction of the impurities with the rare-earth (RE) atoms. This leads to a preferred deactivation of the latter resulting in a decrease of the rare-earth (RE) sublattice magnetization. Moreover, the uniaxial magnetic anisotropy is primarily based on the single ion anisotropy of the Tb atoms. If these are deactivated Ku decreases. At increasing impurity concentrations the selectivity of deactivation decreases and increasing amounts of Fe are affected. Thus, the steepest decrease of Tcomp and Ku is observed at low concentrations. For Tcomp the mean values of the slopes at concentrations below 1 at. % are 35 K per at. % for nitrogen, 85 K per at. % oxygen (Ar/oxygen atmosphere), or 125 K per at. % oxygen (Ar/water atmosphere). Ku is reduced to half its original value at concentrations of 4 at. % nitrogen, 1.2 at. % oxygen (Ar/O2), and 0.9 at. % oxygen (Ar/H2O) in the films. The Curie temperature TC decreases at a rate of about 10 K per at. % impurity. This is due to the diminishing magnetic interactions at increasing impurity incorporation.