Mössbauer spectroscopy of Cr(110)/Fe(110)/Cr(110) sandwiches

Abstract

Magnetic order in ultrathin Fe(110) films in a Cr(110) matrix and its temperature dependence were analyzed using conversion electron Mössbauer spectroscopy (CEMS). The samples were characterized by flat interfaces, as tested by SPA-LEED (spot profile analysis LEED). Fe films consisting of D atomic layers with 1 ≤ D ≤ 31 were doped by 57Fe probes and analyzed using CEMS in situ in UHV, for 100 K ≤ T ≤ 450 K. All spectra could be fitted by Zeeman sextets with B hf( T) following Bloch laws. For films with 2 ≤ D ≤ 6, the first Fe layer in the CrFe interface shows a reduced ground state hyperfine field of B s(0) = 25.8 T, which differs from values determined previously for rough interfaces. It agrees roughly with the predictions from an alloy model. Spin-wave parameters are reduced in comparison with samples W(110)/Fe/Ag. For thicker films ( D > 6), two subcomponents of the interface can be distinguished, with equal abundance, but different hyperfine fields and different b parameters; apparently they belong to two magnetically inequivalent states resulting from the antiferromagnetic order in Cr. Extraordinary low values for the surface enhancement of the b parameters, α s, a = 1.5 and α s, b = 1.1, respectively, and a large value of 10 atomic distances for the interaction length are explained by the antiferromagnetic order of the matrix. The low values for the surface enhancement of the spin-wave parameters differ strongly from results reported for the case of rough interfaces. For the double layer, a break of B hf( T) was observed near the Néel temperature of Cr. Parameters of the monolayer could be roughly determined.