Effect of chromium antiferromagnetism on the magnetic structure of Fe/Cr multilayers

The effects of exchange interaction of electron spins near the interface between iron and chromium layers, VFe-Cr, on the orientation of magnetic moments of iron layers, M-Fe, in multilayered Fe/Cr films are analyzed. In the first approximation in VFe-Cr, the effect of chromium antiferromagnetism on the M-Fe vectors is equivalent to the well-known effect of unidirectional anisotropy. The effect weakens with worsening quality of Fe/Cr interfaces; in this case, the role of effects of second order in VFe-Cr increases. Two types of effects quadratic in VFe-Cr are analyzed. The first one is the effect of induced magnetic anisotropy with an easy axis oriented perpendicularly to the axis of unidirectional anisotropy. The second type is the indirect interaction of M-Fe vectors through the chromium interlayer, which is analogous to the indirect interaction between nuclear spins in antiferromagnets. It is shown that the well-known result of changeover from the ferromagnetic to antiferromagnetic ordering observed upon a change in the number of atomic layers in the chromium interlayer by unity (short-period oscillation in the magnetic structure) in terms of the model suggested is due to the effect of unidirectional anisotropy. Conditions are formulated under which the combined action of linear and quadratic effects in VFe-Cr leads to the appearance of a noncollinear magnetic structure of multilayered Fe/Cr films. It is shown that the change in the number of nodes in the spin-density wave in the chromium interlayer by unity also leads to a changeover from the ferromagnetic ordering of M-Fe vectors to the antiferromagnetic one (long-period oscillation in the magnetic structure).