Journal of Magnetism and Magnetic Materials 272–276 (2004) 1219–1220 Structural characterization of epitaxial Fe/Cr multilayers using anomalous X-ray and neutron reflectivity A. Gupta a,1 , A. Paul a , M. Gupta a , C. Meneghini b , U. Pietsch c , K. Mibu d , A. Maddalena e , S. Dal To ! e e , G. Principi e, * a Inter-University Consortium for DAEF, University Campus, Khandwa Road, Indore 452 017, India b Dipartimento di Fisica, Universit " a di Roma 3, Roma, Italy c Institut f . ur Physik, Universit . at Potsdam, Potsdam, Germany d Research Center for Low Temperature and Materials Sciences, Kyoto University, Kyoto 611-0011, Japan e INFM and Settore Materiali, DIM, Universit " a di Padova, via Marzolo 9, Padova I-35131, Italy Abstract The interface structure of epitaxial Fe/Cr multilayers was studied using anomalous X-ray and neutron reflectivity. The analysis of X-ray reflectivity at three different energies provided a reliable information about the interface roughnesses. It is found that the Cr-on-Fe interface is more diffused as compared to the Fe-on-Cr interface and that the roughness exhibits a significant increase with increasing depth. The magnetic roughness, as determined from neutron reflectivity, is lower than the geometrical roughness, in conformity with the behavior of a number of magnetic thin films and multilayers. r 2004 Elsevier B.V. All rights reserved. PACS: 75.47.De; 61.10.Kw; 61.12 Keywords: Magnetic multilayer; GMR; Reflectivity; Interface roughness; Magnetic roughness Interface alloying in GMR multilayers is known to affect significantly their magnetic properties like strength of bilinear coupling, phase of short wavelength oscillations, etc. [1]. A definite correlation has been observed between interface roughness and strength of GMR [2] and extensive studies have been done on the interface structure, especially in the Fe/Cr system [3–5]. In the present work, X-ray and neutron reflectivity has been used for elucidating the interface structure in epitaxial Fe/Cr multilayers. Multilayers having the structure MgO(001) sub- strate/Cr10nm/[Fe3nm/Cr1.2nm] Â 20 were prepared using e-beam evaporation in a UHV chamber. X-ray reflectivity of the multilayers was measured at the GILDA beamline of ESRF, Grenoble at three different photon energies, namely, 5.989keV (just below the absorption edge of Cr), 7.111keV (just below the absorption edge of Fe) and 10.0 keV. Polarized neutron reflectivity measurements were done at ADAM beam- line, ILL, Grenoble. Fig. 1 gives the X-ray reflectivity patterns of the multilayer at the three different energies. It may be noted that, due to the large difference in the refractive indices of Fe and Cr at the three energies, the three reflectivity patterns are significantly different from each other. Therefore, a simultaneous fitting of these curves can provide unambiguous information about the inter- face structure. Moreover, the average absorption coefficient of the multilayer increases significantly with X-ray energy, being 79.5 cm 2 /g at 5.989 keV, 136.2 cm 2 /g at 7.111 keV and 165.6 cm 2 /165.6cm 2 /g at 10.0 keV. As a consequence, the X-rays penetration depth in the multilayer will decrease significantly with increasing the X-ray energy. Eventually, the three measurements together also provide some depth selective information about the interface structure. ARTICLE IN PRESS *Corresponding author. E-mail addresses: agupta@iucindore.ernet.in (A. Gupta), giovanni.principi@unipd.it (G. Principi). 1 Also for correspondence. 0304-8853/$-see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.058