Magnetic properties of Co/Rehcp(101¯0)superlattices

Abstract

hcp(101 0) Co/Re superlattices were grown via magnetron sputtering on Al 2 O 3 (112 0) substrates. The thickness of the Co layers 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 conditions the interfacial roughness is approximately 0.4 nm in each material at each interface. High angle x-ray diffraction, together with offspecular x-ray diffraction, showed that the growth is epitaxial with the ͓0001͔ axis in-plane and parallel to the Al 2 O 3 ͓0001͔ axis. Magnetization measurements indicate the presence of an in-plane uniaxial anisotropy in all samples and 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 ferromagnetic 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 transition 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 is positive for small fields and negative for large fields when the current is perpendicular to the applied field. We also report a magnetoresistance of ϳ4.5% at 10 K, more than twice the maximum value previously reported for hcp͑0001͒ Co/Re multilayers. Co/Re hcp(101 0) superlattices provide a new system whereby the role of in-plane magnetic anisotropy in the magnetoresistance of metallic superlattices can be studied.

Out-of-plane exchange bias and magnetic anisotropy in MnPd/Co multilayers

“…It is likely because the large entropy for these interfacial layers would disorder the Co layers, thus lowering its magnetization. This magnetization disordering mechanism is similar to that observed in Co/Re multilayers [20]. Another possibility is that the strains may give rise to the less crystallinity for Co layers.…”

Structure and magnetic properties of Co grown on yttria-stabilized cubic zirconia substrates

“…For example, Re, W, and Nb were utilized for many researchers as the seeding layers for preparing high quality Co and Fe films. 2,3 It is noted that the magnetic properties of films will strongly depend on the film structure and the underlying templates ͑substrates or buffer layers͒. 4,5 In this study, cubic zirconia (ZrO 2 ) stabilized with 9.5 mol % Y 2 O 3 ͑YSZ͒ with ͑100͒ and ͑110͒ crystal orientations was chosen as a substrate to study the growth condition for Co films.…”

Large in-plane anisotropies in Co/Re superlattices: What’s happening at the interface?

“…High angle x-ray diffraction shows that the superlattices are epitaxial, with the ͓0001͔ direction parallel to the substrate's c axis which lies in the film plane and the ͓101 0͔ lies parallel to the growth direction. 4 Fits to an optical model 5 of the low-angle true specular reflectivity give the actual layer thickness and interface roughness, shown in Table I.…”

“…4 A 50 Å buffer layer of Re was deposited at 560°C followed by the growth of the 20 bilayer Co/Re superlattice at 158°C. Four superlattices were grown with a nominal Re thickness of 10 Å and varying Co thickness.…”