Double-spiral magnetic structure of the Fe/Cr multilayer revealed by nuclear resonance scattering

摘要

We have studied the magnetization depth profiles in a [57Fe(dFe)/Cr(dCr)]x30multilayer with ultrathin Fe layers and nominal thickness of the chromiumspacers dCr 2.0 nm using nuclear resonance scattering of synchrotron radiation.The presence of a broad pure-magnetic half-order (1/2) Bragg reflection hasbeen detected at zero external field. The joint fit of the reflectivity curvesand Mossbauer spectra of reflectivity measured near the critical angle and atthe "magnetic" peak reveals that the magnetic structure of the multilayer isformed by two spirals, one in the odd and another one in the even iron layers,with the opposite signs of rotation. The double-spiral structure starts fromthe surface with the almost antiferromagnetic alignment of the adjacent Felayers. The rotation of the two spirals leads to nearly ferromagnetic alignmentof the two magnetic subsystems at some depth, where the sudden turn of themagnetic vectors by ~180 deg (spin-flop) appears, and both spirals start torotate in opposite directions. The observation of this unusual double-spiralmagnetic structure suggests that the unique properties of giantmagneto-resistance devices can be further tailored using ultrathin magneticlayers.