Figure 1: Static magnetic properties of Eu_1−xGd_xO films.

(a) Dependence of T_C (ref. 22, solid triangles) and of the square root of the static MSHG intensity (open squares with grey line as guide to the eye) on the carrier density n_c at 4.2 K in Eu_1−xGd_xO. The inset shows the relationship of the Gd concentration to n_c (ref. 22). All error bars represent the s.e.m. and the uncertainty in the film thickness in determining n_c from the Hall measurements. (b) Sketch of the spin- and energy-dependent density of states of undoped ferromagnetic EuO near the bandgap²⁰. The Eu 5d6s conduction band is split by the 4f–5d exchange interaction. States not shown like 4f minority, 5de_g and oxygen 2p are off the scale. The MSHG process probes the magnetic order via a two-photon transition to the 5d6s conduction band. (c) Temperature dependence of for undoped and 2.65% Gd-doped EuO.