STRUCTURE AND MAGNETISM OF BCC-FE CO MULTILAYERS STUDIED BY MEANS OF PERTURBED-ANGULAR-CORRELATION SPECTROSCOPY/

We have used perturbed angular correlation spectroscopy to study Fe/Co superlattices grown on(1-10)-GaAs with a Co thickness around 20 Angst rom and Fe thicknesses between 10 and 40 Angstrom. We found that all h yperfine fields in these layers are along the [110]-axis in the plane of the multilayers. Measurements of the temperature dependence of the Cd hyperfine field at the center of the (1-10)-Co layers were interpre ted in terms of gradually changing Co-structure. Below the growth temp erature, thermal lattice expansion accounts for the anomalous temperat ure dependence of the hyperfine field. At higher temperature the monoc linic deformation of the Co lattice gradually relaxes until a nearly u ndeformed BCC-structure is achieved around 570 K. Further increasing t he temperature causes a phase transition of the Co lattice that result s in interdiffusion of Fe and Co. These results in accordance with the oretical calculations suggest that the BCC-like Co structure is stabil ized by an interfacial energy contribution, particularly by lattice st rain and that BCC-Co is not a thermodynamically metastable phase. We r esolved satellite hyperfine fields that are unambiguously attributed t o probe atoms in plateaus near a sharp interface. In addition, broad f requency distributions associated with a diffuse interface were obviou s in the data. Therefore, we proposed a growth model for (1-10)-Fe/Co where interfaces of Co on top of Fe are sharp and those of Fe on top o f Co are diffuse. Within the extended Steams hyperfine-field model, th e hyperfine-field data were interpreted in terms of magnetic moments. The moment profile derived for (1-10)-Fe/Co reveals a Friedel oscillat ion of both the Fe and Co near interface moments. The spatial variatio n of the moments is best described by an amplitude, decaying exponenti ally with the distance to the interface and modulated by a sine functi on of the same distance. Between 90 and 570 K, the amplitude, the deca y constant and the wave vector of the modulation are constant within t he values determined. The Friedel oscillation of the near interface mo ments is understood as due to spin waves traveling across the interfac e and interfering with those of the penetrated lattice. The experiment al results suggest that the nodes of the spin waves should be pinned t o the interface. The resulting oscillation is superimposed on the bulk moment. This picture evidently explains why the experimental moment p rofile at(1-10)-Fe/Co is symmetric about the interface.