Magnetization depth dependence and reversal processes in exchange coupled FeF$_{2}$/F (F=Fe,Ni,Py) bilayers

Antiferromagnet-ferromagnet (AF-F) bilayers exhibit exchange bias effect, i.e. a shift of the F hysteresis loop after a cooling down below the Ne\'{e}l temperature of the AF. We use SQUID magnetometry and magneto-optical Kerr effect (MOKE) to study the magnetization depth dependence and reversal processes in the F layer of FeF$_{2}$(70nm)/F(70nm) (F=Fe, Ni, Py) samples. Since the MOKE penetration depth is about 35nm for F layer, it is possible to achieve depth dependent information on the F probing both sides of the layer. Analyzing the SQUID response arising from the whole sample and MOKE hystesis loops from both AF-F and air interfaces we show that a magnetic structure perpendicular to the interface is created in the F layer near the AF-F interface. The compression of this magnetic structure with the external field is a reversible process. Work supported by US-DOE.