Tunneling Spectroscopy in Ferromagnetic Semiconductors

The observation of zero-bias anomalies in tunneling has received much attention but their interpretation has suffered from a lack of definition of the character of the tunneling barrier. Junctions formed from a metal with Eu-chalcogenide ferromagnetic semiconductors offer a potential means of overcoming this difficulty. We have made rectifying junctions of EuS:Eu on In. The results indicate: 1) a large resistivity peak at zero-bias voltage which, in the ferromagnetic region, has a strong magnetic-field dependence, and 2) a resistance maximum near 30 mV which has been tentatively assigned to excitation of collective modes in the bulk of the semiconductor. We interpret the present results by considering excitation of ferromagnetic magnons in the barrier region.