Growth, morphology, and structure of a monolayer thickGdFe2surface alloy

R P Williams,S G Alcock,P B Howes,C L Nicklin

doi:10.1103/physrevb.94.075419

Abstract

The growth and structure of an ordered ${\mathrm{GdFe}}_{2}$ surface alloy deposited on Mo(110) has been studied using in situ surface x-ray diffraction. Growth curves and reflectivity scans of varying ratios of Gd to Fe show how the two species intermix prior to alloy formation. After annealing to form the ordered surface alloy, in-plane x-ray diffraction data indicate that the Fe atoms are laterally displaced along the [001] or $[00\overline{1}]$ direction by $0.16\ifmmode\pm\else\textpm\fi{}0.02$ \AA{} from the long bridge site positions. Out-of-plane crystal truncation rod analysis reveals that the Gd atoms lie $3.40\ifmmode\pm\else\textpm\fi{}0.09$ \AA{} above the Mo(110) bridge site, an expansion of 22% relative to the expected hard sphere distance. This is significantly larger than observed in previous studies of the growth of pure Gd on Mo(110). Simple geometric changes are not able to account fully for this expansion and we propose that hydrogen incorporation during alloy formation may also contribute.

Highlights

The growth of ultrathin magnetic films continues to be the subject of much research attention, motivated by possible applications for future magnetic recording devices
Simple geometric changes are not able to account fully for this expansion and we propose that hydrogen incorporation during alloy formation may contribute
Gradmann et al [1] reported on the epitaxial growth of Fe(110) on W(110) at 500 K using low energy electron diffraction (LEED) and Auger electron spectroscopy (AES), reporting that one monolayer (ML) of Fe grew pseudomorphically by Frank–van der Merwe (FM) layer-bylayer growth

Summary

Introduction

The growth of ultrathin magnetic films continues to be the subject of much research attention, motivated by possible applications for future magnetic recording devices. Previous surface x-ray diffraction studies by Meyerheim, Popescu, and co-workers [2,3] of Fe on W(110) show pseudomorphic growth in the initial layers together with interlayer contractions and the onset of tensile stress with second layer formation. They showed that for a thick (13 ML) film, satellite peaks can be attributed to a periodic arrangement of misfit dislocations. Tikhov et al [4] studied Fe, Co, and Ni on a Mo(110) surface and found that for all cases pseudomorphic FM growth occurred at room temperature, island or Stranski-Krastanov (SK) growth at elevated temperatures while alloying was observed for thicker films at higher temperatures.

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Discussion

Conclusion