Anisotropy of the sublattice magnetization and magnetoresistance in Co/Re superlattices on Al2O3(11(2)over-bar0)

[Co(20 Angstrom)/Re(6 Angstrom)](20) superlattices were grown on a (11 (2) over bar 0) surface of a Al2O3 single crystal, with the [0001] direction of their hcp structure in the plane of the film. The Co layers were found to be antiferromagnetically coupled (AF), with a saturating field of 6 kOe. Po larized neutron reflectivity was used to determine the direction of the sub lattice magnetization. In zero applied field, the AF moments are aligned al ong the Co[0001] axis. In a magnetic field H perpendicular to the Co[0001] axis, the sublattices moments evolve to a canted arrangement, with the AF c omponent always perpendicular to the field. With H along the Co[0001] axis, the AF moments flop in a direction perpendicular to Co[0001] axis. The spi n flop transition is not abrupt, but can be described as a gradual rotation that is completed at 2 kOe. The anisotropy of the sublattice magnetization is related to the anisotropy of the magnetoresistance. This has the conven tional dumbbell behavior with the field applied perpendicular to the Co[000 1] axis, but exhibits an extended plateau near H=0, and a slight increase u p to H similar to 2 kOe, when H is parallel to Co[0001] axis. (C) 1999 Amer ican Institute of Physics. [S0021-8979(99)18708-5].