Mossbauer studies of the surface and bulk magnetic structure of scandium-substituted Ba-M-type hexaferrites

A direct comparison of the magnetic structures of a surface layer and of th e bulk of Ba-M-type hexagonal ferrites with iron ions partially replaced by Sc diamagnetic ions (BaFe12-xScxO19) has been made by simultaneous Mossbau er spectroscopy with detection of gamma rays, characteristic x-ray emission , and electrons. It has been found that, if the magnetic lattice of a Ba-M- type hexagonal ferrite is weakly diluted by Sc diamagnetic ions, a similar to 300-nm thick macroscopic layer forms on the surface of a BaFe11.4Sc0.6O1 9 crystal, in which the iron-ion magnetic moments are noncollinear with the moments in the bulk. The noncollinear magnetic structure forms in the near -surface layer of BaFe12-xScxO19 crystals because the exchange interaction energy is additionally reduced by the presence of such a "defect'' as the s urface. This is the first observation in ferromagnetic crystals of an aniso tropic surface layer whose magnetic properties, as predicted by Neel, diffe r from those of the bulk. (C) 1999 American Institute of Physics. [S1063-78 34(99)02203-0].