Control of Spin-Density-Wave Magnetic Structures using Interface Effects

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The spin structure (magnetic structure) of Cr, which is a typical material having a "spin-density-wave" magnetic structure, was controlled using interface effects. Bulk Cr has a body-centered cubic (bcc) structure and, below the magnetic transition temperature of 311 K, shows a spin-density-wave antiferromagnetic structure, where the spin magnetic moments align parallel in each bcc (001) plane and antiparallel between adjacent bcc (001) planes and modulate sinusoidally with a period of 6 to 8 nm. Epitaxial Cr/X multilayers, which have a structure where monatomic layers of element X are periodically embedded in a Cr film, were grown by ultrahigh-vacuum deposition and the spin structures were examined by neutron diffraction and Mossbauer spectroscopy. It was found that novel spin structures, which are not observed in bulk Cr, appear in the multilayers due to the pinning of antinodes or nodes of spin-density-wave modulation at the embedded X atoms through interface effects. The spin structures were dependent on the sort of the inserted element and thus can be controlled by selecting the counter element. It was also found that the spin structures of bcc (001)-oriented Cr/X multilayers and those of bcc (011)-oriented multilayers are quite different even when the Cr layer thickness is the same. These results are interpreted by the competition between the "nesting effect" and the interface effect. In this way, it was demonstrated that spin-density-wave magnetic structures can be controlled by making use of the interface effects.