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

摘要

Superlattices of Co/Cr have been epitaxially sputtered onto MgO (100) and (110) substrates coated with 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(bar 1)00)/bcc-Cr(211) superlattice structures are formed. On MgO(100)/Cr(100), XRD suggest strained hcp-Co(11(bar 2))/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 on 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(sup 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(sup 3) at 10(angstrom) Cr thickness. Modest GMR values no larger than 3% are observed and we find no evidence of enhanced AMR effects recently reported for Co(1(bar 1)00)/Cr(211) superlattices.