Influence of the Cr and Ni concentration in CoCr and CoNi alloys on the structural and magnetic properties

The crystalline and magnetic properties of micron thick magnetron sputtered Co1-xCrx and Co1-xNix alloy films are analyzed in the view of their implementation as semi-hard magnets. All of the tested films crystallize in an hcp lattice, at least up to 35 at% of alloying elements (Cr or Ni). The structural study shows that the ratio of hcp phase with [0001] axis orientated perpendicular to the film as compared with in-plane orientation increases (resp. decreases), when Ni (resp. Cr) concentration increases independently of the post-annealing temperature. The orientation of the magnetization results from the competition between the demagnetization field which tends to align the magnetization in plane and the crystalline anisotropy which tends to maintain the magnetization along the [0001] axis. Interestingly, we find that, although Co and Ni are very similar atoms, Co1-xNix alloys crystalline anisotropy can be strongly increased and reach up to twice the anisotropy of the best Co1-xCrx alloy, while maintaining a magnetization at saturation above 1200 kA/m. The thermal stability of the structural and magnetic properties of both alloys is demonstrated for an annealing temperature up to 300 degrees C. (C) 2016 Elsevier B.V. All rights reserved.