Relationship between stoichiometry and properties of EuO films

Abstract

The preparation of EuO films by co-evaporation of Eu and Eu 2O3 has been studied. The two most important parameters to control are the ratio r=Eu/Eu2O3 and the background pressure. The latter should be in the 10-6-Torr range, and only by starting with high density (>95%) Eu2O3 is it possible to maintain this. As r increases from 0.8 to 1.4 we observe the following: (1) A large increase in Tc is observed from 51°to 117°K; (2) the absorption a increases from 0.85×105/cm to 1.6×10 5/cm and the peak shifts toward the red (from 5900 to 6000 Å); (3) the longitudinal Faraday rotation 2φ (with 25° incident angle at 6328 Å) increases from 0.9×105 deg/cm to a maximum of 3.7×105 deg/cm, followed by a slight decrease; and (4) H c (10°K) decreases sharply from 140 Oe to a minimum of 43 Oe for r=0.94, followed by a slight increase. The best films which were single-phase stoichiometric EuO, with bulk-like properties, are obtained with r=0.94. These have well-defined x-ray diffraction patterns with lattice constants a 0=5.14 Å, Tc of 71°K, and the normal Faraday rotation (at 20°K with H=20 kOe) of 8.5×105 deg/cm. In films with r>0.9 the increase of Tc is attributed to the presence of Eu-metal which contributes conduction electrons to enhance the Eu 2+Single Bond signEu2+ interaction. For r<0.9, films with a0=5.10 are obtained which have Tc=51°K. We propose a model where the Eu2+Single Bond signEu2+ exchange interaction is weakened by the formation of a metastable solution of Eu3+ in the EuO lattice. These new results will be compared with previously published data. © 1970 The American Institute of Physics.