Preparation and structure of Fe-doped EuO films

A large increase in ferromagnetic Curie temperature from 69.5°K to ∼190°K has been observed in EuO films doped with Fe. These films retain most of the large magneto-optic rotation of EuO (at 4.2°K) desired for beam addressable memories. However, the increase in T_c permits the operation of these devices at the more convenient liquid-nitrogen temperature. Films were prepared by simultaneous evaporation of Eu, Eu₂O ₃, and Fe at pressure of 2×10^-5 Torr. The amount of T_c increase is strongly dependent upon composition. For example, films with the highest T_c require Fe/Fe+Eu∼0.07 and excess Eu with a typical weight ratio of Eu/Eu₂O₃∼1.3 as compared to ∼0.9 for pure EuO. The analysis by Seeman-Bohlin x-ray diffractometer shows the same NaCl structure as that of pure EuO with a slightly larger lattice parameter (5.1564 Å). The doping also causes a reduction of grain size (from 200 to 120 Å) and a tendency toward preferred orientation. Results of electron microprobe spectroscopy and Mössbauer measurements show that the iron is predominantly present in the metallic state and the europium in the Eu^{+ +} state. The dependence of physical properties on fabrication parameters will be critically examined. © 1971 The American Institute of Physics.