MOLECULAR PHYSICS REPORTS 40 (2004) 89-94 ION MODIFICATION OF THE MAGNETOTRANSPORT PROPERTIES OF Fe/Cr MULTILAYERS M. KĄC 1,2 , M. TOULEMONDE 2 , J. JAWORSKI 1 , J. JURASZEK 3 , R. KRUK 1 , S. PROTSENKO 4 , V. TOKMAN 1 , AND M. MARSZAŁEK 1 1 The Henryk Niewodniczański Institute of Nuclear Physics PAN Radzikowskiego 152, 31-342 Kraków, Poland 2 CIRIL (CEA-CNRS-ENSICAEN), BP5133, 14070 Caen Cedex 05, France 3 Groupe de Physique des Matériaux, UMR6634-Université de Rouen, BP12 avenue de l'université 76801 Saint Etienne du Rouvray cedex, France 4 Sumy State University, R.-Corsakova, 2, 40007 Sumy, Ukraine Abstract: The Cr thickness corresponding to the first antiferromagnetic maximum (1.2 nm) was chosen as a spacer in (Fe/Cr)20 multilayers. Magnetotransport properties of as-deposited Fe/Cr multilayers measured by four probe method at room temperature shown magnetoresistance (MR) effect around 2.2%. Structural, magnetic and magnetotransport properties of Fe/Cr multilayers were modified by irradiations with 163 MeV Au ions with fluence ranging form 1 × 10 11 to 5 × 10 12 ions/cm 2 . Conversion Electron Mössbauer Spectroscopy (CEMS) indicated increasing, with irradiation fluence, mixing at the interfaces. Irradiations resulted also in monotonic decrease of MR as a function of fluence. 1. INTRODUCTION The magnetic properties of Fe/Cr multilayers have been a subject of intensive study due to their relevance in fundamental science and technology. The observation of antiferromagnetic coupling between two Fe layers separated by Cr spacer [1], oscillations of this coupling in magnitude (with a long ~1.2 nm and short period ~0.3 nm) as a function of the Cr spacer thickness [2-4], and giant magnetoresistance (GMR) effect [5, 6], were all first reported for Fe/Cr systems. The GMR is closely related to the antiferromagnetic exchange coupling of Fe layers through the non magnetic spacer layer. The transition from antiparallel (at remanence) to parallel alignment induced by externally applied magnetic field changes the scattering probabilities of spin-up and spin-down electrons and results in a decrease of the resistivity. The electronic transport in layered thin films is determined by combined effect of the elec- tronic structure of the two metals (Fe, Cr in discussed samples), as well as by the micro- structure of the interface [7]. Some theoretical descriptions show that interface roughness can enhance or reduce the GMR [8]. It was found experimentally that GMR increases substantially with increasing interfacial roughness [9]. However, in contrast to these results, it was also observed that increasing interfacial roughness causes GMR to decrease [10] and a very large GMR (220% at 1.5 K) has been found in Fe/Cr multilayers with smooth interfaces [11]. It is well known that interface roughness can be affected by deposition conditions of multilayer structure [9] or by post-deposition treatments like thermal annealing [12, 13] and ion irradia- tion [14, 15]. Ion irradiation may lead to the increase of the GMR [14] as well as to the de- gradation of the GMR [10] depending on the applied ions and fluences. In this paper, we present study of the structural and magnetotransport properties of Fe/Cr multilayers irradiated at room temperature with 163 MeV Au ions.