Reciprocal exchange bias and exchange spring effects in the Heisenberg antiferromagnet RbMnF3 interfaced with a permalloy film

Among the important phenomena that arise from the interfacial exchange interaction between different magnetic materials are exchange bias (EB) and exchange spring (XS). The exchange bias occurs between ferromagnetic (FM) and antiferromagnetic (AF) materials, and its main manifestation consists of a shift of the hysteresis loop of the FM layer along the field axis. The exchange spring is observed when two FM materials are in contact, producing a single hysteresis loop combining the properties of the two. Experiments to study the EB effect are usually carried out with AF/FM bilayers in which both films are very thin. Here we report the observation of the reciprocal exchange bias effect in a thick single-crystal slab of the Heisenberg AF RbMnF₃ interfaced with a very thin film of the soft FM permalloy (Ni₉₁Fe₁₉, Py). Measurements of the magnetic moment versus applied magnetic field in a wide temperature T range (5--300 K) reveal a hysteresis loop of the AF material shifted along the field axis in the positive direction. For thicker Py films that have a magnetic moment comparable to that of the AF slab, we observe XS effects. Interestingly, both effects manifest in the AF phase of RbMnF₃ (T<830.16em0exK) as well as in the paramagnetic phase up to room temperature.