Helical and Incommensurate Spin-Density Waves in Fe/Cr Multilayers with Interfacial Steps

Abstract

Although absent in bulk transition metals, a noncollinear, helical (H) spin-density wave (SDW) is stabilized by steps at the interfaces in Fe/Cr multilayers. Using the random-phase approximation, we evaluate the phase boundary between the H SDW and the collinear, incommensurate (I) SDW found in bulk Cr. In agreement with neutron-scattering results, the I-to-H transition temperature T{sub IH} is always lower than the bulk N{acute e}el temperature T{sub N} and the nodes of the I SDW lie near the Fe-Cr interfaces. While a H SDW with a single {plus_minus}{pi}/2 twist has lower free energy than a I SDW above T{sub N} , H SDW{close_quote}s with larger twists are stable between T{sub IH} and T{sub N} . {copyright} {ital 1998} {ital The American Physical Society }