Magnetism of Thin Epitaxial Cr-Films in Sandwich Structures and Superlattices. Hartmut Zabel, Institut für Experimentalphysik/Festkörperphysik, Ruhr-Univeristät Bochum, D-44780 Bochum, German
Neutron and synchrotron scattering experiments will be presented on the spin structure in thin epitaxial Cr films revealing the effects of scaling and proximity to neighboring ferromagnetic layers. The spin density wave (SDW) magnetism of thin epitaxial Cr films has recently been the focus of interest because of its mediating role in exchange coupled superlattices and GMR materials. While the incommensurate SDW and the Néel temperature TN are well established for bulk Cr [1], the question arises of how these properties are altered in thin films and superlattices with magnetic layers. We have recently carried out extensive synchrotron and neutron scattering experiments to probe the commensurate and incommensurate SDWs and to establish phase diagrams as a function of Cr film thickness. We will review these results starting with pure Cr(001) films, which exhibit an increased period of the incommensurate SDW and an enhanced TN as compared to bulk Cr [2]. For Cr films covered with thin Fe layers the transverse incommensurate SDW propagates in the film plane with the Cr spins pointing out-of-the plane [3]. Thus the Fe and Cr magnetic moments are oriented perpendicular to each other. This can be understood as a frustruation effect due to monatomic steps at the Fe/Cr interface. With decreasing Cr thickness, the propagation direction of the transverse SDW changes direction into the out-of-plane direction in order to gain exchange energy at the interface. Finally, as the Cr thickness drops below the modulation period, only a commensurate antiferromagnetic state remains [4]. In this state strong oscillatory type exchange interaction between Fe layers separated by Cr layers can be observed, together with non-collinear alignments of the Fe magnetization vectors [5].
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2. P. Sonntag et al. Phys. Rev. B 52, 7363 (1995); submitted Phys. Rev. B
3. P. Bödeker et al. JAP 81, Apr. 15, 1997; to be published
4. A. Schreyer et al. PRL, submitted
5. A. Schreyer et al. P R B 52, 16 066 (1995); J.F. Ankner, JAP 81 (1997)