Direct observation of Cr spin polarization in epitaxial Cr/Co/Cr(100) trilayers

The spin polarization of chromium at the interface next to a ferromagnetic layer is of general interest because of the competing ferromagnetic and antiferromagnetic exchange coupling. While the Fe/Cr interface has been well studied, information on the Co/Cr interface still remains scarce. Here we show for epitaxially grown Cr/Co/Cr(100) trilayers with smooth interfaces x-ray resonant magnetic scattering (XRMS) results in a saturation field of +/- 270 mT, recorded at the Co and Cr L-3 edges, respectively. The XRMS results at the Co edge show the expected asymmetry and a ferromagnetic hysteresis for different incident angles.. Furthermore, XRMS measurements with the energy tuned to the Cr L-3 edge also exhibit an asymmetry, albeit much smaller than the one at the Co L-3 edge. Moreover, the magnetic hysteresis of Cr taken at the L-3 edge has a sign opposite to that of Co at the L-3 edge over a broad range of incident angles. From these results we infer first that at the Co/Cr interface chromium is ferromagnetically polarized, and second that its spin structure is oriented opposite to the magnetization of Co.