MOSSBAUER INVESTIGATIONS OF THE SURFACE-STATE OF HEXAGONAL FERRITES SR-M NEAR THE CURIE-POINT

The temperature dependence of the parameters of the hyperfine interact ion in the surface layers and in the bulk of macroscopic crystals of h exagonal ferrites of the type Sr-M (SrFe12O19) is investigated by the method of simultaneous gamma-, x-ray, and electron Mossbauer spectrosc opy. It is shown experimentally that the transition of an similar to 2 00 nm thick surface layer of macroscopic ferromagnets to the paramagne tic state occurs at a temperature 3 degrees below the Curie point (T-C ) for the bulk of the crystal. It was established that the transition temperature T-C(L) of a thin layer localized at a depth L from the sur face of the crystal increases away from the surface and reaches the va lue T-C at the lower (away from the surface) boundary of the so-called ''critical'' surface layer. A nonuniform state in which the bulk regi on of the crystal is magnetically ordered while the surface region is disordered is observed near T-N. (C) 1998 American Institute of Physic s. [S0021-3640(98)01911-2].