Anisotropy of the sublattice magnetization and magnetoresistance in Co/Re superlattices on Al₂O₃(1120)

Abstract

[Co(20 Å)/Re(6 Å)]₂₀ superlattices were grown on a (1120) 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. Polarized neutron reflectivity was used to determine the direction of the sublattice magnetization. In zero applied field, the AF moments are aligned along 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 component 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 spin 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 conventional dumbbell behavior with the field applied perpendicular to the Co[0001] axis, but exhibits an extended plateau near H=0, and a slight increase up to H∼2 kOe, when H is parallel to Co[0001] axis.