Journal of Magnetism and Magnetic Materials 226}230 (2001) 1776}1778 Mo K ssbauer study of Fe/Ag multilayers on Cu(100) R. Paniago*, J.L. Lo H pez, H.-D. Pfannes Departamento de Fn & sica, Universidade Federal de Minas Gerais, C.P. 702, 30123-970 Belo Horizonte, Brazil Abstract Fe/Ag multilayers composed of ultrathin layers were grown on Cu(100) in ultrahigh vacuum by molecular beam epitaxy. Magnetic analysis of the Fe-layers (95% enriched in Fe) was performed by in situ conversion electron Mo K ssbauer spectroscopy at room temperature and 100K. Samples with di!erent thicknesses of the Ag-spacers (2}3 monolayers) as well as with di!erent thicknesses of the Fe-layers were prepared in order (a) to determine whether the magneticorientation(in-plane/outofplane)ofthe Fe-layersischanged,(b)tostudyitsin#uenceontheintensityofthe hyper"ne magnetic "eld and (c) to identify superparamagnetism due to small Fe islands inside the layers.  2001 Published by Elsevier Science B.V. Keywords: Iron "lms; Multilayers; Conversion electron Mo K ssbauer spectroscopy; Superparamagnetism The study of magnetic orientation and the size of magnetic moments in ultrathin metallic "lms and multi- layered systems has been the subject of many investiga- tions.InthisworkFe/AgmultilayersgrownonCu(100) are studied by in situ Fe conversion electron Mo K s- sbauer spectroscopy. Because of the extremely low solu- bilityofFeinAgandviceversa,itispossibletoproduce high quality Ag/Fe multilayers with very low mixing at the interfaces. The samples were grown in a molecular beam epitaxy (MBE)system.Filmgrowthwasmonitoredbyre#ection high-energy electron di!raction (RHEED), the clean- less by X-ray photoelectron spectrscopy (XPS) and angle-resolved ultraviolet photoelectron spectroscopy (ARUPS). The Cu(100) crystal was previously cleaned and prepared by argon ion sputtering (1.3keV) and an- nealing at 6003C until sharp spots in the low-energy electron di!raction (LEED) pattern indicated a well or- dered surface. The multilayers were grown under ultra highvacuumconditionbyevaporationofsilverandiron from molybdenum and alumina crucibles, respectively, typically at a rate of 1 monolayer (ML) per minute. First let us take a look at the superlattice formation. The growth of silver on the Cu(100) between 2}5ML * Corresponding author. Fax: #55-31-499-5600. E-mail address: paniago@"sica.ufmg.br (R. Paniago). coverage is so that this system exhibits a well ordered c(102)Ag/Cu(100)structure.Withthesilveratomsar- rangedinaslightlystrainedhexagonalarray,thegrowth of Ag occurs in the (111) direction [1]. Indeed the ARUPS spectrum (not shown here) of a 5ML overlayer ofAgonCu(100)lookslikethespectrumoftheAg(111) monocrystal.WeexpectthegrowthofFeonAg(111)to be in the (110) direction since the small mis"t( ( 1%) guarantees good epitaxy. Fe(110)/Ag(111) multilayers have been produced by a number of authors and some Mo K ssbauer data collected in transmission mode are well known [2}5]. Our RHEED/LEED analysis con"rms Fe(110)/Ag(111) multilayer formation. InTable1the "ttedMo K ssbauerparametersofsamples A, B and C, characterised by the composition [(Ag  /Fe  )  /Ag  ]/Cu(100)], where n is the number of Ag/Fe multilayers, are given. On growing samples A, B, C we started with x monolayersofAgonCu(100),and thenwegrew(n times) y monolayers of Fe and x mono- layersofAg.Wegrewalso(sampleI)abilayerofFeand Ag which showed nice RHEED oscillations during the growth of 7ML of Fe on Ag  /Cu(100). Sample Ishoweda6-lineMo K ssbauer spectrum (not shown here) with an isomer shift characteristic for the BCC (or even BCT) structure. We conclude that our Fe layer grew in the BCC(110) direction. According to our Mo K ssbauer spectra (Figs. 1 and 2) and their parameters (see Table 1) we can draw some 0304-8853/01/$-see front matter  2001 Published by Elsevier Science B.V. PII:S0304-8853(01)00072-5