Surface magnetism of Sc-substituted Ba-M hexaferrites

A technique of simultaneous gamma-ray, x-ray, and electron Mossbauer spectr oscopy is used to study the magnetic structure of the surface layer with di rect comparison to the magnetic structure inside single crystal samples of hexagonal Ba-M ferrites, in which part of the iron ions have been replaced by diamagnetic Sc ions (chemical formula BaFe12-deltaScdeltaO19). It is fou nd that when the diamagnetic Sc ions are introduced into the crystal lattic e of BaFe12-deltaScdeltaO19 at concentrations (x = 0.4 and 0.6) far below t he level at which the collinear magnetic structure inside the sample is des troyed, a macroscopic layer of thickness similar to 300 nm develops on the surface, in which the magnetic moments of the iron ions are oriented noncol linearly with respect to the moments inside the sample. The deviation <thet a > of the magnetic moments in BaFe11.6Sc0.4O19 was 10 degrees +/- 2 degree s for x = 0.4, and when the Sc concentration was raised to 0.6, the angle < theta > increased to 17 degrees +/- 2 degrees. The noncollinear magnetic st ructure in the surface layer in these crystals develops because of further reduction in the energy of the exchange interactions owing to the presence of a "defect," such as the surface. For the first time, therefore, an aniso tropic surface layer whose magnetic properties differ from those in the int erior of a sample has been observed experimentally in ferromagnetic crystal s, as predicted by Neel [L. Neel, Phys. Radium. 15, 225 (1954)]. (C) 1999 A merican Institute of Physics. [S1063-7761(99)01111-7].