Magnetic field effect on the optical absorption edge in ferromagnetic EuO

We have investigated the magnetic field dependence of the transmission and piezotransmission spectra around the absorption edge in ferromagnetic EuO. The piezo-transmission spectra display a sign inversion versus temperature. This sign inversion disappears under application of a small magnetic field which induces also a significant shift of the absorption spectrum. These phenomena cannot be simply explained by a magnetic field ordering of domains. A two bands absorption model, involving both4f \rightarrow 5dand4f \rightarrow 6soptical transitions is proposed and discussed.