Interface modification in Fe/Cr epitaxial multilayers using swift heavy ion irradiation Ajay Gupta * , Dileep Kumar UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452 017, India Available online 20 December 2005 Abstract Effect of 100 MeV Au ions irradiation on the interface structure and magneto transport properties of Fe/Cr epitaxial multilayers: MgO(0 0 1)/Cr (100 A ˚ )/[Fe (30 A ˚ )/Cr (12 A ˚ )] 20 , have been studied. Interface structure is characterized by X-ray reflectivity and X-ray diffuse scattering measurements. In order to enhance the contrast between Fe and Cr layers, measurements are done at the X-ray energy just below the absorption edge of the iron. Diffuse scattering measurements show that the irradiation results in a substantial decrease in the in-plane correlation length of the roughness, while the roughness itself changes only by a small amount. Further, measurements at different values of q z suggest that the variations take place mainly in the uncorrelated part of the roughness. Giant magnetoresistance measurements in the irradiated multilayer suggest that it is mainly affected by the change in root mean square roughness and is influenced only weakly by variation in the in-plane correlation length. Ó 2005 Elsevier B.V. All rights reserved. PACS: 75.70.Cn; 75.47.De; 61.10.Kw; 61.80.Jh Keywords: Magnetic multilayers; Interface roughness; Diffused scattering; GMR 1. Introduction Magnetic multilayers exhibiting GMR like Fe/Cr are important because of their application in magnetic storage devices as well as read–write heads. While the basic theory of GMR in idealized magnetic multilayers is well devel- oped, the effects of various imperfections in real multilayers are not at all properly understood. Effect of interface roughness on giant magneto resistance (GMR) in Fe/Cr multilayers has been a subject of considerable interest. A number of studies have been done in recent years with an aim to study the effect of interface structure on GMR [1– 5]. It has been found that generally the GMR decreases with increasing interface roughness. The observed change in the GMR with roughness can be attributed to two differ- ent factors: (1) variation in the interlayer coupling and (2) variation in the spin dependent scattering at the interfaces [6–8]. However, the interface roughness is not the only parameter for characterizing the interface structure in mul- tilayers. The other parameters, which are important for complete characterization of interface structure, are interdiffusion and in-plane correlation length. In case of multilayers, another quantity of interest is the correlation between the height variations of successive interfaces. The total roughness r consists of two components; the corre- lated roughness r c and the uncorrelated roughness r u ðr 2 ¼ r 2 c þ r 2 u Þ. As shown in Fig. 1, generally the uncorre- lated part of the roughness has a smaller in-plane corre- lated length n u as compared to that of the correlation part of the roughness n c [9]. In the present work the interface structure of epitaxial Fe/Cr multilayers has been varied by irradiation with swift heavy ions and the resultant effect on the magneto trans- port properties has been studied. Effect of irradiation on the interface roughness as well as in-plane correlation length of both correlated and uncorrelated part of the 0168-583X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.11.021 * Corresponding author. E-mail address: agupta@csr.ernet.in (A. Gupta). www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B 244 (2006) 202–205 NIM B Beam Interactions with Materials & Atoms