Synthesis and Magnetic Properties of Non-Equilibrium Eu-Rich EuO Thin Films

EuO thin films have been formed by reactive evaporation, in which O2 gas was introduced in the form of a molecular beam directed toward a substrate. In order to optimize preparation conditions, we varied the substrate temperature, T s, and the ratio of the Eu vapor to O2 gas deposition rates, R. The structure and magnetic properties of the films were measured by X-ray diffraction and a super-conducting interference device (SQUID) magnetometer. Non-stoichiometric EuO films can be produced more easily at T s=200° C than at T s=300° C. Choosing an appropriate value of R at T s=200° C, we obtain Eu-rich EuO films with the Curie temperature of about 150 K. The present method is based on the control of reaction kinetics, and is superior to the post-oxidation method of Eu-metals with respect to the formation of Eu-rich EuO films.