Anisotropy studies of AFM coupled MBE grown Co/Cu(001) superlattices

Abstract

We have studied the anisotropy behavior of antiferromagnetically (AFM) coupled fcc Co/Cu(001) sandwiches and superlattices. Magneto-optical Kerr effect measurements on samples with Cu film thicknesses in the range of the second antiferromagnetic maximum reveal characteristic shapes of the hysteresis loops in close agreement with theoretical predictions. For the AFM coupled samples we infer antiparallel spin orientations in remanence perpendicular to the originally applied magnetic field direction. Changing the magnetic layer thickness and maintaining a constant thickness of the spacer completely alters the shape of the hysteresis loops. The loops of weakly coupled AFM layers show characteristic steps, indicative for a rather unusual nonsymmetric spin state. This behavior can be explained by the competing effects of anisotropy with the exchange coupling.

Magnetic phases and reorientation transitions in antiferromagnetically coupled multilayers

“…In fact, a great number of novel mag-netic configurations and remarkable reorientational effects in external fields have been found in such superlattices. [9,10,15,17] In particular, recent experimental results using modern depth-resolving techniques reveal spatially inhomogeneous magnetic structures, e.g. in Fe/Cr(001) superlattices, [17] and specific reorientation effects imposed by four-fold planar (tetragonal) anisotropy.…”

“…Superlattices with planar magnetization grown on (001) faces of cubic substrates, e.g. multilayers from materials combinations as Co/Cu [9], Fe/Si [10,11] Co/Cr, [12,13,14] or Fe/Cr, [15,16,17] belong to this class. In the case of weak four-fold anisotropy, their magnetic properties are mostly determined by the interlayer exchange interactions which may include an important biquadratic contribution.…”

“…[2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17] Such layered synthetic antiferromagnets can be separated into two classes according to the symmetries ruling their magnetic properties: Superlattices with relatively strong uniaxial anisotropies include low-symmetry multilayers with effective uniaxial magnetic anisotropy in the layer planes, e.g. epitaxial systems deposited on (110), (211) faces of cubic substrates.…”

“…Strong effective four-fold anisotropies have been found in systems such as Co/Cr(001) or Fe/Cr(001). [9,13,14,15] The competition between magnetic anisotropy, applied fields and exchange energies may cause complicated magnetic effects and processes. In fact, a great number of novel mag-netic configurations and remarkable reorientational effects in external fields have been found in such superlattices.…”

“…[3,8,15,21,22,23] These studies have demonstrated the general validity of the phenomenological models to describe the magnetization processes in antiferromagnetic nanostructures. [3,8,9,17] For the system under discussion the phenomenological theory has been developed to describe effects of 90 degree couplings and a concomitant complex evolution of domain structures in Fe/Cr/Fe layers. [24] Four-fold anisotropy effects have been theoretically investigated in Ref.…”