Surface spin-flop transition in epitaxial Co/Re superlattices

Two hcp [Co/Re](x) superlattices were grown simultaneously on (11 (2) over bar0) Al2O3 single crystal substrates, where the number of bilayers x=20 and 21. The film growth was epitaxial in nature with the [0001] of the substrate aligned with the [0001] of the superlattice. The film interface roughness and thickness were determined by x-ray reflectivity to be sigma=4.4 Angstrom, t(Re)=8 Angstrom, t(Co)=20 Angstrom for x=20 and t(Co)=16 Angstrom for x=21. The Co layers were antiferromagnetically coupled with an easy axis along the [0001]. As expected, the 20-bilayer superlattice exhibited both surface and bulk spin-flop transitions, while in the 21-bilayer superlattice only the bulk spin-flop transition was observed by magneto-optic Kerr effect measurements. The magnetoresistance (MR) with Hparallel to[0001] shows an extended plateau around H=0 with Hperpendicular toI, where H is the applied magnetic field and I the sensing current. The layer-by-layer magnetization profile was found using energy minimization techniques and the MR was calculated using an empirical model. The calculations compare favorably with the MR data allowing the separation of anisotropic magnetoresistance and giant magnetoresistance components to the MR. (C) 2003 American Institute of Physics.