Magnetic properties of epitaxial Co/Pd superlattices

Abstract

A series of Co/Pd superlattices with constant Pd layer thickness of dPd = 11 Å were grown on single-crystal GaAs(110) substrates by molecular beam epitaxy (MBE). A buffer layer of 500 Å of Pd provided an atomically smooth, fcc(111) single-crystal starting surface for the superlattice deposition. The resulting superlattices maintain this crystal symmetry and smoothness throughout their epitaxial growth. Details of the structural characterization of these samples are given elsewhere in these proceedings. The magnetic properties of these films have been measured by vibrating sample magnetometry. A perpendicular easy axis is found for all seven of the superlattices presented (dCo = 2, 4, 8, 10, 12, 17, and 20 Å). An unusually high coercive field of Hc = 6.6 kOe is observed for dCo = 2 Å, and decreases monotonically with increasing dCo. The saturation magnetization agrees well with a model composed of bulk Co layers with an additional contribution from polarized Pd. The uniaxial magnetic anisotropy energy can be described by both an interface term and a large volume term favoring a perpendicular easy axis for dCo < 23 Å. Comparisons with a series of polycrystalline multilayers simultaneously deposited on Si substrates reveal significant differences in the magnetic behavior.