Mössbauer investigations of the surface state of hexagonal ferrites Sr-M near the curie point

Abstract

The temperature dependence of the parameters of the hyperfine interaction in the surface layers and in the bulk of macroscopic crystals of hexagonal ferrites of the type Sr-M (SrFe12O19) is investigated by the method of simultaneous gamma-, x-ray, and electron Mossbauer spectroscopy. It is shown experimentally that the transition of an ≈ 200 nm thick surface layer of macroscopic ferromagnets to the paramagnetic state occurs at a temperature 3° below the Curie point (Tc) for the bulk of the crystal. It was established that the transition temperatureTc(L) of a thin layer localized at a depthL from the surface of the crystal increases away from the surface and reaches the valueTc at the lower (away from the surface) boundary of the so-called “critical” surface layer. A nonuniform state in which the bulk region of the crystal is magnetically ordered while the surface region is disordered is observed nearTN.