Preparation and Structure of Fe-Doped EuO Films

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Abstract
A large increase in ferromagneticCurie temperature from 69.5°K to ∼190°K has been observed in EuO filmsdoped 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 Tc permits the operation of these devices at the more convenient liquid‐nitrogen temperature. Films were prepared by simultaneous evaporation of Eu, Eu2O3, and Fe at pressure of 2×10−5 Torr. The amount of Tc increase is strongly dependent upon composition. For example, films with the highest Tc 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.