Abstract
Relation among structure of Ru underlayer and atomic layer stacking structure and uniaxial magnetocrystalline anisotropy (Ku) of sputtered Co films was discussed. Small torque with amplitude below theoretical limit |KuCobulk-2π(MsCobulk)2| = 6.8×106 erg/cm3 was obtained for Co film with thickness dCo ＜ 30 nm deposited on rough Ru underlayer. Structure analysis of the thin Co films with dCo ＜ 30 nm deposited on rough Ru underlayer demonstrated that: 1) Magnitude of stacking faults were less than 1%, which meant the Co films had almost perfect hcp stacking, 2) Lattice constant c was expanded about 0.6% with retaining lattice constant a, 3) Thin Co films had rough surface which reflected morphology of the Ru underlayer. According to these results, it was thought that initial Co growth reflected vertical stacking of Ru underlayer on inclined crystal plane of the rough Ru underlayer. Ku was derived by correcting torque amplitude with self-demagnetizing energy considering surface morphology of Co film. Ku took maximal value of 5.0×106 erg/cm3 at dCo = 30 nm, and rapidly decreased with decreasing dCo. Reduction of Ku in dCo ＜ 30 nm might be caused by decrement of crystallographic uniaxial anisotropy for Co film due to expansion of the c axis.
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