Mössbauer spectroscopical investigation of the exchange biased Fe/MnF₂ interface

Two different Fe/MnF₂ samples have been prepared by e-beam evaporation on MgO(001) substrates. The Fe layer in the samples includes a 10 Å thick ⁵⁷Fe probe layer either at the Fe/MnF₂ interface (interface sample) or 35 Å away from the interface (center sample). The samples are characterized by X-ray diffraction, conversion electron Mössbauer spectroscopy (CEMS) and SQUID magnetometry. ⁵⁷Fe CEMS has been employed to study the depth dependent hyperfine interactions in Fe/MnF₂ as a function of temperature between 18 K to 300 K. The hyperfine field B_hf has been obtained for the interfacial and off-interfacial ⁵⁷Fe layers. At the interface, besides B_hf of bcc-Fe, the presence of a component with a distribution P(B_hf) is observed. The latter is assigned to interfacial ⁵⁷Fe atoms, indicating some (∼15%, equivalent to ∼1 Fe atomic layer) intermixing at the Fe/MnF₂ interface and a decrease of the average <B _hf > by 21%. The influence of the interface disappears as the ⁵⁷Fe probe layer is placed away from the interface. The temperature dependence of the average <B_hf > of the interface has been measured. The Fe spins, at remanence, are found to lie in the film plane.