Magnetic properties of Co Re hcp(10(1)over-bar0) superlattices

hcp(10 (1) over tilde 0) Co/Re superlattices were grown via magnetron sputt ering on Al2O3(11 (2) over bar 0) substrates. The thickness of the Co layer s was approximately 1.8 nm with the Re layer thickness varying between 0.5 nm and 3.0 nm. Low angle x-ray reflectivity revealed that for our growth co nditions the interfacial roughness is approximately 0.4 nm in each material at each interface. High angle x-ray diffraction, together with off-specula r x-ray diffraction, showed that the growth is epitaxial with the [0001] ax is in-plane and parallel to the Al2O3[0001] axis. Magnetization measurement s indicate the presence of an in-plane uniaxial anisotropy in all samples a nd antiferromagnetic coupling when the Re layer thicknesses are less than 1 .0 nm and close to 2.0 nm. The uniaxial anisotropy was measured via ferroma gnetic resonance and determined to be approximately 5 times smaller than in bulk Co for thicker Re layer samples. For thin Re samples, a spin-flop tra nsition causes a competition between the anisotropic magnetoresistance and the giant magnetoresistance when the external field is applied parallel to the easy axis. The most notable consequence is that the magnetoresistance i s positive for small fields and negative for large fields when the current is perpendicular to the applied field. We also report a magnetoresistance o f similar to 4.5% at 10 K, more than twice the maximum value previously rep orted for hcp(0001) Co/Re multilayers. Co/Re hcp(10 (1) over tilde 0) super lattices provide a new system whereby the role of in-plane magnetic anisotr opy in the magnetoresistance of metallic superlattices can be studied. [S01 63-1829(99)00317-3].