Surface magnetism during the early stages of oxygen-assisted growth of Cr on Fe(001): A SPMDS study R. Moroni * , F. Bisio, M. Canepa, L. Mattera Unit  a INFM and CFSBT, Dipartimento di Fisica, Universit  a di Genova, via Dodecaneso 33, I-16146 Genova, Italy Abstract The surface magnetic properties of ultrathin Cr films grown on O(1  1)-Fe(001) have been studied by means of spin-polarised metastable de-excitation spectroscopy (SPMDS). The spin-selected surface density of states extracted fromtheexperimentalSPMDSdataprovidesinformationonbothcompositionandmagneticpropertiesofthetopmost layer.WefindthatoxygenfloatsonthesurfaceofthegrowingCrfilmandthatCr/Feintermixingisrestrictedtothe first Cr layer. Concerning the magnetic properties, a strong polarisation of Cr 3d electrons is found in agreement with theoretical calculations. Oxygen 2p states are polarised too and their polarisation is opposite to that of Cr 3d states. Surface magnetisation as a function of the Cr film thickness shows an oscillatory behaviour induced by the layered antiferromagnetic structure of Cr. At variance with the results of other experimental investigation in this case the layered antiferromagnetic structure of Cr is already present in the 3 ML thick film. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Magnetic measurements; Magnetic surfaces; Chromium; Iron; Oxygen Inthelastdecadetherehavebeenanumberof theoretical and experimental studies aimed at elu- cidating the magnetic structure of Cr films grown on Fe(001). This strong interest is partly mo- tivated by the mediating role of Cr spacers in exchange coupled superlattices [1] and giant mag- netoresistance materials [2]. Besides the techno- logical interest, the magnetic properties of thin Cr films on Fe(001) rise more fundamental ques- tions of how their magnetic structure is altered either due to reduced dimensionality or to prox- imity with the ferromagnetic substrate [3]. In fact, either the broken symmetry in the direction nor- mal to the film or the interface exchange and hybridisation effects may strongly influence the magnetic structure in this system. The magnetic structure of thin Cr films on Fe(001)canbeassessedbymeasuringthesurface magnetisation of the Cr film as a function of its thickness.Clearly,inordertoperformthiskindof experimentitisnecessarytodisposeofatechnique sensitive exclusively to the magnetisation of the topmost layer [4,5]. Otherwise, the contribution induced by the presence of the substrate and un- derlying Cr layers must be evaluated and sub- tracted to the measured signal [6–9]. Another method to determine the magnetic structure consists in exploiting its effect on the exchange coupling of Fe/Cr/Fe(001) trilayers. Nuclear Instruments and Methods in Physics Research B 193 (2002) 480–484 www.elsevier.com/locate/nimb * Corresponding author. Tel.: +39-10-353-6287; fax: +39-10- 311-066. E-mail address: moroni@fisica.unige.it (R. Moroni). 0168-583X/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0168-583X(02)00824-8