Exchange coupling through spin-density waves in Cr(001) structures: Fe-whisker/Cr/Fe(001) studies

Exchange coupling through a spin-density wave in Fe-whisker/Cr/Fe(001) stru ctures has been studied using Brillouin light scattering (BLS) and magneto- optical Kerr effect (MOKE). The Fe-whisker(001) substrates provide nearly i deal templates: they are characterized by atomic terraces having dimensions in excess of several micrometers. Such templates are essential for the stu dy of short-wavelength exchange coupling which is mediated by the intrinsic spin-density wave in Cr(001). Atomically smooth Cr(001) layers similar to those of the Fe-whisker surfaces can be grown at raised substrate temperatu res. Angular resolved auger electron spectroscopy measurements have shown t hat the Fe-whisker/Cr(001) interfaces are affected by an atom exchange plac ement mechanism (interface alloying). It will be shown that this interface alloying at the Fe-whisker/Cr interface profoundly affects the behavior of the short-wavelength oscillations. The phase of the short-wavelength oscill ations is reversed compared to that expected for the spin-density wave in C r(001), The strength of coupling is significantly decreased from that obtai ned from first-principles calculations, and the first crossover to antiferr omagnetic coupling occurs at 4 ML. BLS and MOKE have shown unambiguously th at the exchange coupling in Fe-whisker/Cr/Fe(001) structures can be describ ed by bilinear and biquadratic terms. Experiments carried out using Cu and Ag atomic layers between the Cr(001) and Fe(001) films, i.e., heterogeneous interfaces, have shown that the exchange coupling in Cr(001) is strongly a ffected by electron multiple scattering. It will be argued that the exchang e coupling through thick (>8 ML) and atomically smooth Cr(001) spacers can be described by localized interactions (Heisenherg type) and by electron mu ltiple-scattering (quantum well state) contributions. This is in good accor d with recent first-principle calculations by Mirbt and Johansson. However, interface alloying severely affects the behavior of the exchange coupling for Cr thicknesses less than 8 ML. In this thickness regime the overall cou pling exhibits mostly a long-wavelength behavior with a small superimposed short-wavelength contribution. This initial Cr thickness regime is responsi ble for changes in the phase of the short-wavelength oscillations and for t he reduced strength of the exchange coupling due both to the localized and to the multiple-scattering contributions. We have observed no significant d ependence of the exchange-coupling strength on the Fe film thickness for sa mples having the structure Fe-whisker/11Cr/nFe/20Au where n specifies an ir on film thickness between 5 and 40 ML. However, preliminary data show that the exchange coupling is significantly increased in specimens for which bot h sides of the iron film are covered by Cr, i.e., for structures of the for m Fe-whisker/11Cr/nFe/11Cr/20Au. It appears that electron resonant states i n the iron film play no important role in the strength of the exchange coup ling when the iron is bounded on one side by the gold, but that they do bec ome important when the iron film is bounded by Cr on both sides. BLS and MO KE studies on Fe-whisker/Cr/Mn/Fe/(001) samples revealed that the antiferro magnetic state of Mn is composed of compensated (001) atomic plants. The re sults of the above experimental studies will be compared to recent theories . Points of agreement and of disagreement between the experimental results and recent first-principles calculations will be explicitly pointed out. [S 0163-1829(99)10921-4].