Spin-Resolved Tunneling Studies of the Exchange Field in EuS/Al Bilayers

We use spin-resolved electron tunneling to study the exchange field in the Al component of EuS/Al bilayers, in both the superconducting and normal-state phases of the Al. Contrary to expectation, we show that the exchange field, Hex, is a non-linear function of applied field, even in applied fields that are well beyond the EuS coercive field. Furthermore the magnitude Hex is unaffected by the superconducting phase. In addition, Hex decreases significantly with increasing temperature in the temperature range of 0.1-1 K. We discuss these results in the context of recent theories of generalized spin-dependent boundary conditions at a superconductor/ferromagnet interface.