Journal of Magnetism and Magnetic Materials 279 (2004) 202–209 Structural and magnetic properties of Al doped Co–Ag granular films: temperature dependence of magnetoresistance R. Mustafa . Oks . uzoglu a, *, Ayhan Elmali b ,R . udiger Henn c , Hartmut Fuess d , Horst Hahn d a Faculty of Science and Art, Department of Physics, University of Selcuk, Campus, Konya 42031, Turkey b Faculty of Engineering, Department of Engineering Physics, Ankara University, Besevler, Ankara 06100, Turkey c Max-Planck-Institut f . ur Festk . orperforschung, Heisenbergstr. 1, Stuttgart D-70569, Germany d Institute for Materials Science, Darmstadt University of Technology, Petersenstrasse 23, Darmstadt D-64287, Germany Received 28 August 2003; received in revised form 21 January 2004 Abstract The correlation between the structure, the magnetic and magnetotransport properties of sputter-deposited (Co 90 Al 10 ) x Ag 100x granular films (19pxp45) are investigated. For an (Co 90 Al 10 ) content of about 28% the magnetoresistance(MR)ratioofthefilmsreachitshighestvalueof6%.AldopingreducestheMRratioinCoAgfilms, however, leads to a almost constant MR ratio against post annealing up to 773K in (Co 90 Al 10 ) 28 Ag 72 granular films, although the film structure is affected by annealing, respectively. According to magnetization measurements, superparamagnetic cobalt grains in the as-deposited (Co 90 Al 10 ) 28 Ag 72 sample show after annealing up to 773K both superparamagneticandferromagneticbehaviour.Annealingat823Kcausesadomainformationoflargeferromagnetic grains with strong correlation. r 2004 Elsevier B.V. All rights reserved. PACS: 75.47.De; 75.70.Cn; 68.55.Jk; 81.15.Cd Keywords: Magnetoresistance; Magnetic properties of heterostructures; Structural properties; Sputtering 1. Introduction The giant magnetoresistance (GMR) effect in magnetic multilayers and subsequently in mag- netic heterogeneous alloys with ferromagnetic granules embedded in nonmagnetic metals has been intensively studied over the last 10 years [1– 8]. In particular, the CoAg granular films, exhibit- ing the largest GMR value at room temperature, were extensively investigated [1,4,8,9–12].Ingran- ular systems, the GMR effect is caused by spin- dependent scattering at the interfaces between the ferromagnetic grains and the nonmagnetic matrix and spin-dependent scattering within ferromag- neticgrains [13,14].Inaddition,theGMReffectis influenced by the size of ferromagnetic grains [8]. As annealing causes grain growth the thermal ARTICLE IN PRESS *Corresponding author. Tel.: +0090-332-223-1844; fax: +0090-332-241-0604. E-mail address: rmoksuzoglu@selcuk.edu.tr (R.M. . Oks . uzoglu). 0304-8853/$-see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.01.080