Influence of surface on the effective magnetic fields in alpha-Fe2O3 and FeBO3

First measurements of the effective magnetic fields as a function of the de pth at which the iron ions are in the surface layer of alpha-Fe2O3 and FeBO 3 single crystals are reported. The method used is the depth-selective conv ersion-electron Mossbauer spectroscopy. An analysis of experimental spectra revealed that the magnetic properties of the crystal surface vary smoothly from the bulk to surface characteristics within a layer similar to 100 nm thick. The layers lying below similar to 100 nm from the surface are simila r in properties to the bulk of the crystal, and their spectra consist of na rrow lines. The spectral linewidths increase smoothly as one approaches the crystal surface. The spectra obtained from a similar to 10-nm thick surfac e layer consist of broad lines indicating a broad distribution of effective magnetic fields. Calculations show that the field distribution width in th is layer is delta = 2.1(3) T, for an average value H-eff = 32.2(4) T. It ha s been experimentally established that, at room temperature (291 K), the ef fective magnetic fields smoothly decrease as one approaches the crystal sur face. The effective fields in a 2.4(9)-nm surface layer of alpha-Fe2O3 crys tals are lower by 0.7(2)% than the fields at the ion nuclei in the bulk of the sample. In the case of FeBO3, the effective fields decrease by 1.2(3)% in a surface layer 4.9(9) nm thick. (C) 2000 MAIK "Nauka /Interperiodica".