Atomic structure in amorphous and multilayered films: Origins of magnetic anisotropy (invited) (abstract)

Abstract

To understand the microscopic mechanism for the magnetic anisotropy, a description of the atomic structure, particularly structural anisotropy, is a crucial first step. Here is described an observation of structural anisotropy by synchrotron x-ray-diffraction experiments on two notable magneto-optical materials having perpendicular anisotropy, namely sputter-deposited amorphous TbFeCo films and 〈111〉-oriented Co/Pt multilayered films. In the as-deposited Tb26Fe62Co12 films, the scattering intensity I(Q) were measured with the scattering vector Q nearly perpendicular and nearly parallel to the film plane. Structural anisotropy was observed to be uniaxial and anelastic, suggesting the presence of the bond-orientational anisotropy, or an anisotropic distribution of the nearest-neighbor bond orientation. In a multilayered Co (3 Å)/Pt (18 Å) film epitaxially grown on a GaAs 〈111〉 substrate, scattering intensity was measured for the scattering vector Q covering a plane with a major component perpendicular and a minor component parallel to the film plane. The diffraction peaks were found to have a large width parallel to the film plane, indicating that there is strong in-plane disorder. Atomic interdiffusion was evaluated from the first two superlattice peaks by integrating the intensity in the film plane of the 〈111〉-oriented film, and was found to be similar to the 〈001〉-oriented film where magnetic easy axis is in the film plane. In the 〈111〉-oriented Co/Pt, however, a Lorentzian peak shape of the intensity distribution in the film plane was observed, indicating the presence of uniaxial structural defects creating 1/r strain field in the film plane. Both types of structural anisotropy could be responsible for the perpendicular magnetic anisotropy.