Magnetic anisotropy, coupling, and transport in epitaxial Co/Cr superlattices on MgO(100) and (110) substrates

Superlattices of Co/Cr have been epitaxially sputtered onto MgO(100) and (110) substrates coated with epitaxial Cr(100) and (211) buffer layers. The Co thickness is fixed at 20 Angstrom and the Cr thickness varied from 7 to 22 Angstrom. On the MgO(110)/Cr(211) substrates, coherent hcp-Co(<1(1)over bar 00>)/bcc-Cr(211) superlattice structures are formed. On MgO(100)/Cr(100), x-ray-diffraction results suggest strained hcp-Co(11(2) over bar)/bcc-Cr(100) superlattices. Magnetization measurements show fourfold magnetic in-plane anisotropy for the MgO(100) orientation and twofold for the MgO(110). By utilizing a simple model based upon perpendicular uniaxial anisotropies, we have concluded that the fourfold anisotropy has its origin in the second-order uniaxial Co anisotropy energy. The antiferromagnetic interlayer coupling strength exhibits a maximum value of 0.15 erg/cm(2) at a Cr thickness of 13 Angstrom in the MgO(110) orientation. The MgO(100) orientation exhibits its strongest coupling of 0.55 erg/cm(3) at 10 Angstrom Cr thickness. Modest giant magnetoresistance values no larger than 3% are observed and we find no evidence of enhanced anisotropic magnetoresistance effects recently reported for Co(<1(1)over bar 00>)/Cr(211) superlattices. (C) 1997 American Institute of Physics.