Enhanced magnetic moments in bcc Fe films.

Abstract

We present evidence for enhanced magnetic moments in epitaxial Fe films in proximity with Ag, Au, Cu, and Pd overlayers prepared by molecular-beam epitaxy on singular Ag(001) substrates in a combined study using polarized-neutron reflection (PNR) and ferromagnetic resonance (FMR). Second versions of equivalent samples were investigated in order to test the repeatability of the results, and all PNR measurements were corrected for background and diffuse scattering. Within experimental error, measurements of the absolute value of the magnetic moment per atom made using PNR were found to agree with measurements of the relative magnetization using FMR, and measurements on repeated samples were also found to agree. An average magnetic moment per Fe atom of 2.58\ifmmode\pm\else\textpm\fi{}0.09${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ was determined for a Ag/5.5 ML Fe structure, significantly enhanced from the value of ${\mathrm{\ensuremath{\mu}}}_{\mathrm{Fe}}$=2.33\ifmmode\pm\else\textpm\fi{}0.05${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ obtained for a Ag/10.9 ML Fe reference sample. Corresponding values of 2.48\ifmmode\pm\else\textpm\fi{}0.08${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ and 2.50\ifmmode\pm\else\textpm\fi{}0.10${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ were determined for Cu/5.8 ML Fe and Cu/5.7 ML Fe structures, respectively. Values of the layer averaged moment of 2.66\ifmmode\pm\else\textpm\fi{}0.05${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ and 2.6\ifmmode\pm\else\textpm\fi{}0.2${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ were determined for Pd/5.6 ML Fe and Pd/5.7 ML Fe structures, respectively, assuming that no induced polarization occurs in the interface Pd layers.The degree of enhancement measured in equivalent samples is seen to be in agreement within experimental error. The magnitude of the enhancement (12--20)% we observe in the samples of thickness close to 6 ML is slightly higher than that predicted by recent band-structure calculations, but our results show conclusively that the enhancement can be attributed to the interface atoms. The temperature dependence of the magnetization has also been measured using PNR and the results compared with that predicted from spin-wave theory using FMR measurements of the effective spin-wave gap. Good agreement is found for the Ag/Fe and Cu/Fe systems for which spin-wave gap temperatures of 0.1 and 0.12 K, respectively, are determined by PNR, compared with values of 0.15 and 0.11 K deduced from FMR, where the agreement for Au/Fe is less good. Both FMR and PNR data are consistent with the largest gap occurring for the Pd/Fe interface system but the value of the spin-wave gap determined by FMR is in this case smaller than the value obtained from fitting the PNR data.