Magnetization Loops in Fe/Ag/Fe/Ni(001) Structures
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MAGNETIZATION LOOPS IN Fe/Ag/FelNi(O01) STRUCTURES B. HEINRICH,* Z. CELINSKI,* H. KONNO,*+ A. S. ARROTIT,* M. RUHRIG,** AND A. HUBERT,* *Physics Department, Simon Fraser University, Burnaby, BC, Canada, V5A 1S6 **Institut fiir Werkstoffwissenschaften der Universitiit Erlangen-Niimberg, Martensstr. 7, D-91058 Erlangen, Germany ABSTRACT The lattice reconstructed bcc Ni(001) in Fe/Ni(001) ultrathin layers allows one to engineer films in which the in-plane 4-fold anisotropies and coercive fields can be varied and adjusted according to specific requirements. Magnetization reversals have been studied in layered structures of Fe/Ag/Fe/Ni(001). For Ag(001) interlayers thicker than 13 ML magnetization reversal can proceed in two steps. In these samples the minor loops switch the magnetization of the Fe(O01) layer from the parallel to the antiparallel configurations with respect to the magnetic moment of the Fe/Ni film. Such minor loops exhibit a rectangular behavior with switching fields of 15-25 Oe. The lattice transformed Fe/Ni layers could be useful in spin-valve structures. INTRODUCTION Ni can be grown epitaxially on Fe(001). The first 3 monolayers (ML) follow the bcc stacking with the same lateral spacingI and the same vertical relaxation 2 as is observed for Fe(00 I). After reaching a critical thickness, 3-5 ML, the Ni overlayers transform gradually into a more complicated structure 2 ,3,4 . The transformed "bcc Ni" exhibits the same main features of the Reflection High Energy Electron Diffraction (RHEED) patterns along the (1001 and 1110) azimuths as the Fe(001), but the RHEED patterns corresponding to (110] azimuths show in addition a weak diffraction streak. The additional superlattice streaks are also visible for azimuths away from the (100) and (110) directions. Their complicated angular dependence and SEXAFS 5 studies by Jiang et al. indicate that the Ni transformation is a rather severe distortion of the basic bcc Ni(001) structure. "bcc Ni" overlayers grown on Fe(001) form a unique structure having magnetic properties which are truly different from those observed for bcc Fe((X)I) and pure bcc Ni(O01). FMR measurements played a crucial role in determining the magnetic properties of both the pure bcc and lattice transformed Fe/Ni(001) bilayers 2 ,6. The magnetic moment in Fe/Ni bilayers measured by FMR was significantly greater than that of the Fe layer whether the added layer was the pure bcc Ni(001) or the lattice transformed "bcc Ni". The saturation magnetizations of both forms of bcc Ni, -5 kG, are nearly as large as in fcc Ni 6. This is in agreement with calculations by Moruzzi and Marcus 7 . The presence of pure bcc Ni does not affect the 4-fold in-plane anisotropy of the Fe(001) layer. However, the lattice transformed "bcc Ni" showed remarkable magnetic properties 2 ,4,6 . The 4-fold anisotropies observed in lattice transformed Fe/Ni bilayers far exceeded those observed in regular 3d transition metals and their alloys; e.g., 2Ki/Ms=2.33 kOe in a bilayer with 6 ML of Fe and 15 ML of Ni (6Fe/15Ni) compared
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