UNCORRECTED PROOF Physica B ] (]]]]) ]]]–]]] Magnetization temperature dependence in Fe/Cr superlattices A.A.R. Fernandes a , C.A. Ramos b, *, A. Macedo Teixeira c , E.E. Fullerton d a Physics Department, Universidade Federal de Esp ! ırito Santo, 29060-900 Vit ! oria, ES, Brazil b Centro At ! omico Bariloche and Instituto Balseiro Comision Nacional de Energia Atomica, 8400 S.C. de Bariloche, RN, Argentina c Instituto Militar de Engenharia, Pra - ca Gen Tiburcio, URCA, Rio de Janeiro, RJ, Brazil d IBM Almaden, 650 Harry Road, 95120-6099 San Jose, CA, USA Abstract We report the temperature dependence of the saturation magnetization, M s ðT Þ; of Fe(t)/Cr(40 ( A) superlattices grown on MgO(100) and MgO(110) and its variation with Fe-layer thickness (5 ( Aoto80 ( A). The structure was characterized by X-ray diffraction. M s ðtÞ vs. T ; as measured by DC magnetization and ferromagnetic resonance, show a large interface effect. The origins of this effect are discussed. r 2002 Published by Elsevier Science B.V. Keywords: Fe/Cr superlattices; Shape anisotropy Since the discovery of the GMR effects in Fe/Cr superlattices (SL) [1], there has been a large effort in understanding and exploiting the novel proper- ties of these artificial materials. In this area Fe/Cr SL have been one of the most extensively studied, yet an understanding of the observed anisotropies and their temperature (T ) dependence is not complete. One of these properties, the appearance of an uniaxial anisotropy when Fe/Cr SL are grown on MgO(1 1 0), has allowed the study of exchange bias due to the coupling of a ferromag- netic film with an uniaxial antiferromagnetic SL [2]. Such structures avoid the limitations imposed by most antiferromagnets where the surface termination and roughness are crucial in under- standing the exchange bias. Other basic research achievements using these SL include the first experimental demonstration of the surface spin- flop in antiferromagnets [3]. One of the simplest SL applications is to study very thin layers with symmetric boundary condi- tions. Along this line we have recently shown [4] that ferromagnetic resonance (FMR) can clearly distinguish the uniaxial and cubic anisotropies present in [Fe(t)/Cr]/MgO(110) (SL110) and [Fe(t)/Cr)]/MgO(100) (SL100). The Cr spacing, nominally 38 ( A, was chosen so as to have a negligible coupling between the layers. FMR in fact shows that the spectra can be described as characteristic of independent layers. Recently [5], saturation magnetization, M s ðT Þ; studies in Fe/Cu SL showed that surface M s decays 17 times faster than bulk. This was interpreted as due to a large reduction of the Fe– Fe exchange near the interface. In this paper we report an X-ray characterization of the SL110 and SL100 series [4], and M s ðT Þ obtained from magnetization and FMR measurements. This work aims to study the M s ðT ; tÞ evolution and identify the 3D–2D crossover on different sub- strate orientations. ARTICLE IN PRESS 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 3B2v7:51c GML4:3:1 PHYSB : 23554 Prod:Type:COM pp:123ðcol:fig::NILÞ ED:JayashreeSanyasi PAGN: evk SCAN: MANGALA *Corresponding author. Fax: +54-2944-445299. E-mail address: cramos@cab.cnea.gov.ar (C.A. Ramos). 0921-4526/02/$-see front matter r 2002 Published by Elsevier Science B.V. PII:S0921-4526(02)00668-3