AU FE THIN-FILM MAGNETIC MULTILAYER MATERIALS - A LAYER-SPECIFIC STRUCTURAL-ANALYSIS USING MEDIUM-ENERGY ION-SCATTERING/

This paper presents an account of the application of medium-energy ion scattering (MEIS) to the investigation of thin-film metallic multilay ers grown using molecular-beam epitaxy. MEIS can provide high resoluti on compositional and structural information as a function of depth in the near surface region (0-250 Angstrom); these parameters are inextri cably linked with the magnetic properties exhibited by materials of th is type. Amongst the information available from MEIS is the accurate d etermination of the layer spacings, structural information from indivi dual layers (even at thicknesses close to a monolayer), and high sensi tivity to disorder in the layers. MEIS therefore provides additional i nformation above that provided by in situ reflection high-energy elect ron diffraction monitoring during growth and ex situ x-ray diffraction measurements so that it represents an ideal complementary technique f or the analysis of thin-film magnetic multilayer materials of this typ e. An Au/Fe multilayer sample of a type previously shown to exhibit gi ant magnetoresistance (GMR) was analyzed. Individual gold layers were clearly resolved and a measurement of the bilayer spacing obtained; th is parameter determines the magnitude of the exchange coupling and GMR . Au/Fe/Au trilayer samples grown on both MgO(100) and sapphire(11 (2) over bar 0) substrates were also analyzed for a series of Fe layer th icknesses between 2 and 16 Angstrom. The MgO(100) grown samples showed unusually high second-layer Au signal consistent with atomic layer sp acings in the Fe layers that lead to enhanced illumination of the seco nd-layer Au. This effect could be modeled using bcc(100) layer spacing s thus confirming the structure to be bcc(100) Fe between fcc(100) Au layers. In the sapphire-grown samples, twinned fcc(111) structure was observed in the individually resolved Au and Fe layers. The amplitude of the Fe blocking features was reduced with increasing Fe layer thick ness indicating a reduction in crystallinity until for the highest thi ckness there was little indication of structure within the layer. The maximum layer thickness for fcc(lll) Fe growth was seen to lie between 8 and 16 Angstrom.