REORIENTATIONAL TRANSITION OF THE MAGNETIC-ANISOTROPY IN CO CR(001) SUPERLATTICES/

We have measured the magnetic anisotropy of Co/Cr(001) superlattices a s a function of the Co thickness using magneto-optical methods and a t orsion magnetometer. The samples grown by molecular-beam epitaxy exhib it a reorientational transition of the easy axis from in-plane for lar ge Co thicknesses (t(Co) greater than or equal to 15 Angstrom) to out- of-plane for 10 Angstrom less than or equal to t(Co), less than or equ al to 15 Angstrom and back again to the in-plane orientation for t(Co) less than or equal to 10 Angstrom we provide evidence that this reori entational transition of the magnetization direction is due to a sign change of the interface anisotropy constant induced by a concomitant s tructural phase transition of the Co layers from hcp to bcc with decre asing Co layer thickness.