Origin of magnetization-induced uniaxial anisotropy in evaporated Fe-Co and Ni-Co films

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Abstract
The contributions, from (1) strain‐magnetostriction anisotropy due to substrate constraint and (2) directional ordering of atom pairs, to the magnetization‐induced uniaxial anisotropy in evaporated Fe‐Co and Ni‐Co films are considered and their variation with concentration is studied. It is found that iron atoms in Fe‐Co films are not so mobile as to form freely Fe‐Fe pairs aligned parallel to the field applied at the time of deposition or annealing; hence the contribution from directional ordering of atom pairs is limited in these films. The compositional dependence of uniaxial anisotropy in Ni‐Co films for the range 30–100% Ni can be explained by a linear combination of the two mechanisms. In Ni‐Co films the directional ordering of atom pairs contributes more than 90% to the total anisotropy in the range 30–60% Ni. The constant a of Néel‐Taniguchi theory is also found to depend on concentration.