Tunneling Study of $EuS$ Magnetization

Ferromagnetic $EuS$ crystals have Curie temperatures which increase rapidly as a function of electron concentration due to strong indirect exchange between the impurity electron and the localized 4f states. Using measurements of indium vs $EuS$ tunnel junctions, we have obtained the temperature and field dependence of the long range magnetic order (spontaneous moment) and short range fluctuations in this order (magnetic fluctuations). The long range magnetic order splits the conduction band and the resulting band edge shift is reflected in a change in the tunneling barrier height. Thus measurement of the tunneling conductance, dominated below T_c (21.5 K) in the low concentration samples by the barrier height change, is a measure of the temperature and field dependence of the spontaneous moment. Moment data obtained by this method agree to within 5% with Mossbauer and demagnetizing field measurements on the same material. Magnetic fluctuations in the sample cause scattering of the electrons in the barrier which dominate the conductance in the paramagnetic region. A simple model based on electron critical scattering predicts the experimentally found Curie‐Weiss temperature dependence (30 to 300 K) and magnetoconductive term (0–27 kOe): , where $Go$ and $G1$ are constants.