Europium monoxide displays colossal magnetoresistance (CMR) and metal-to-insulator transitions (MIT). Using rare earth doping, its Curie temperature can be increased up to approximate to 170 K, but at the cost of drastically reduced CMR and MIT ratios. A substantial increase of these ratios in Eu0.99La0.01O can be achieved by interfacing it with niobium. Hereby the interface transparency critically depends on the large Zeeman splitting of the Eu0.99La0.01O conduction band.