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Stacking faults ͑SFs͒ in Co-based alloy grains in a Co 100−x M x ͑M: Cr, Mo, and W͒ film are evaluated by means of in-plane x-ray diffraction. Moreover, the correlation between SFs and uniaxial magnetocrystalline anisotropy K u is discussed in connection with the spin-orbit interaction. The ratio of the integrated intensities of the ͑10.0͒ to ͑11.0͒ diffractions corrected by Lorentz and atomic scattering factors has been proposed as an index for SFs in hcp films with a c-plane sheet texture. This ratio is equal to 0.25 for perfect hcp stacking, while it is 0 for perfect fcc specific stacking. It has a one-to-one correspondence with the probability of -A-B-C-atomic-layer stacking P fcc . Using this index, pure sputtered Co films are found to have a P fcc of 10%. The addition of only 5 at. % of Mo or W into the Co grains reduces P fcc to 2%. K u was found to increase with the addition of material ͑e.g., K u was 4.0ϫ 10 6 ergs/ cm 3 for 5 at. % Mo͒, although the atomic magnetic moment of Co decreases monotonously. A P fcc of 10% is found to lower K u in a pure Co film by more than a factor of 2 when the spin-orbit interaction is taken into account.

Co80Ir20 films with negative uniaxial magnetocrystalline anisotropy (Ku) are investigated with respect to the regularity of the stacking sequence and atomic site arrangement. Substrate heating at 600 °C enhances the negative Ku of Co80Ir20 to −9.6 × 106 erg/cm3. X-ray diffraction analysis and scanning transmission electron microscopy of the Co80Ir20 film fabricated at 600 °C indicate (1) a near perfect hexagonal-close-packed (hcp) stacking structure and (2) an atomic layered structure that consists of randomly sequenced Ir-rich and Ir-poor layers. These hcp and composition-modulated atomic layer stacking structures are considered to be the reason for the enhancement of the negative Ku.

The negative uniaxial magnetocrystalline anisotropy (Ku) was evaluated for various compositions of Co100-xIrx thin films with respect to the atomic layer stacking structure. Pure Co film fabricated at a substrate temperature (Tsub) of 600 C was found to have a positive Ku of 6.1×10 6 erg/cm 3 . With increasing x, the sign of Ku changed from positive to negative, and the negative Ku took a maximum value of -9.6×10 6 erg/cm 3 at around x = 20 at. % for films fabricated at Tsub = 600 C. Adding more Ir decreased the absolute value of the negative Ku which became 0 over x = 50 at. %. X-ray diffraction analysis and scanning transmission electron microscopy revealed that the atomic layer stacking structure of the Co100-xIrx films changed from -A-B-A-B-(hcp) to -A-B-C-A-B-C-(fcc) stacking with increasing Ir content. Moreover, Co80Ir20 grains were revealed to consist of 2 kinds of randomly located composition-modulated atomic layers, nearly pure-Co and pure-Ir layers, while Co and Co50Ir50 had disordered structures. In this paper, a new perspective on the atomic layered structure with superlattice diffraction, which is different from the conventional "ordered structure", is discussed.

The magnetic properties and structures of Co80Pt20–30 vol % oxide (ZrO2, Cr2O3, Y2O3, Al2O3, MnO, TiO2, WO2, SiO2, Mn3O4, WO3, Co3O4, MoO3, and B2O3) granular media deposited at room temperature were investigated. As a result, the following were found. 1) By employing oxides with low melting point temperatures as the granular media, magnetic grains with high saturation magnetization ( ) and perpendicular magnetic anisotropy ( ) are obtained; the increases in and are due to the promotion of the columnar growth of magnetic grains and phase separation or two-phase precipitation between magnetic grains and oxides. 2) The increase in the of the granular media followed by the decrease in the melting point of oxides is due to the reduction in the amount of stacking faults. 3) Among these granular media, the CoPt–B2O3 granular medium has the highest coercivity (H c) and ratio of H c to the magnetic anisotropy field ( ) of 8.0 kOe and 0.4, with and of 1115 emu/cm3 and 1.1 × 107 erg/cm3, respectively. 4) The CoPt–B2O3 granular medium has well-isolated and columnar growth magnetic grains with an average grain size of 6.5 nm.