Epitaxial multilayers of ferromagnetic insulators with nonmagnetic metals and superconductors

Novel electronic properties are observed in metals in contact with the ferromagnetic insulator europium monoxide (EuO). The authors have successfully prepared epitaxial bilayers and multilayers involving EuO and the metals V or Ag. With metal layers of 100 angstrom thickness or less, these structures exhibit a slope discontinuity in their resistance versus temperature at 90 K for V/EuO interfaces and at 50 K for Ag/EuO interfaces. For metal layers less than about 40 angstrom, a feature is also apparent in R(T) at 70K, the Curie temperature of bulk EuO. The slope discontinuities are reminiscent of those observed at the Curie temperature of ferromagnetic metals. Kerr effect measurements confirm that the EuO exhibits ferromagnetic ordering at 70 K. In V/EuO structures, the V still displays superconductivity with a slightly depressed transition temperature. This suggests that such metal/ferromagnetic insulator structures may be used to prepare artificial ferromagnetic superconductors. The resistive transition is incomplete, suggesting small regions of isolated superconductivity within the sample, as has been predicted for certain special cases when a superconductor is in proximity to a ferromagnet