X-ray diffraction measurements of lattice strains in Co/Pd(001) superlattices films

Lattice spacings in fcc-Co/Pd(001) superlattice films grown on GaAs(001) substrates with a Ag(001) buffer layer were measured using a four-circle diffractometer. For samples with Co layers thinner than 9 angstrom and Pd layers thinner than 12 angstrom, the observed in-plane (110) lattice spacings were all 2.71±0.01 angstrom, indicating 8.0% lattice expansion of Co layers and 1.5% lattice contraction of Pd layers. The (002) lattice spacings along the growth direction were estimated from a profile fitting method, and they were 1.60±0.02 angstrom for Co layers and 1.98±0.02 angstrom for Pd layers. This means that Co layers are contracted nearly 10%, while Pd layers are expanded 2% along the growth direction of the superlattice films. The estimated large lattice strains are successfully applied to explain the large magnetovolume contribution to the magnetic anisotropy reported previously.