Magnetic and structural properties of nanophase Pt/Co multilayers

We have studied the magnetic and structural properties of Pt/Co multilayers grown on Pt nanoparticles with pre-etched thicknesses 10-50 Angstrom. Unexpectedly, the perpendicular anisotropy energy (K-eff) and coercivity (H-c) were maximum for multilayers grown on 33 Angstrom Pt. K-eff was 1.2 x 10(7) erg/cm(3)-Co and H-c was 3.5 kOe, both exceptionally large for Ar-sputtered Pt/Co multilayers. As revealed by X-ray diffraction, transmission electron microscopy, and scanning tunneling microscopy, their microstructure was comprised of 15-20 nm, physically isolated grains with flat surfaces, or mesas, and superior spatial coherence of their artificially modulated structure. In contrast, the surface structure of multilayers was continuous on thicker (50 Angstrom) Pt, and very rough on thinner (17 Angstrom) Pt. We attributed the larger multilayer anisotropy energy on 33 Angstrom Pt nanoparticles to a larger surface anisotropy contribution, caused by flatter (sharper) Pt/Co interfaces, and the larger coercivity to segregated grains, which pin domain wall motion.