Physica B 318 (2002) 222–230 Annealing effect on structural and magnetic properties of Co-based thin film multilayered structures A. Dinia a, *, F. Bensmina b , D. Muller c a IPCMS-GEMM (UMR 7504 du CNRS), ECPM-ULP, 23 Rue du Loess, 67037 Strasbourg, France b IPCMS-GSI, ULP-CNRS, UMR 7504, 23 Rue du Loess, 67037 Strasbourg, France c Laboratoire Phase, ULP-CNRS, 23 Rue du Loess, 67037 Strasbourg, France Received 12 November 2001; received in revised form 3 January 2002 Abstract We report on the annealing effect on magnetic properties of the interface and bulk structure of Ta 50 ( A/Cu 50 ( A/Co t ( A/Cu 50 ( A/Ta 50 ( A sandwiches, with t ¼ 20 and 75 ( A. The sandwiches were obtained by magnetron sputter-deposited on Si(111) substrates at RT and then high-vacuum annealed at 2401C, 3601C and 4401C during 6.5h. RT magnetometry, plane-view transmission electron microscopy and Rutherford backscattering were used to characterize the properties of the samples. For small Co thickness, annealing up to 4401C leads to a strong reduction of the saturation magnetizationFmore than 50% of the bulk valueFwhereas the coercivity drops from 32Oe to zero. For large Co thickness, annealing causes a reduction of the saturation magnetization by a factor of two but the coercivity increases from 44 Oe up to about 300 Oe. Using different characterization techniques, we show that these results can be explained by layer interdiffusion between Co and Cu and the formation of a granular Co–Cu alloy confirmed by the appearance of magnetoresistance for the annealed sandwiches. r 2002 Elsevier Science B.V. All rights reserved. PACS: 75.70.i; 75.70.Cn; 75.70.Pa Keywords: Spin-valve; Co/Cu; Thin films; Interface; GMR; Interdiffusion 1. Introduction One of the very interesting phenomena that have been discovered in magnetic sandwiches and multilayers is the giant magnetoresistance (GMR) effect. This was first reported by Baibich et al. [1], in 1988, on Fe/Cr multilayers. After- wards, an increasing number of systems have been studied and have shown the GMR effect. Spin valve structures [2] are presently the most studied magnetoresistive structures because of their inter- esting potential for applications in read heads for ultrahigh density recording, magnetic sensors and memories [3]. These systems contain at least one magnetic layer in the stack with a fixed orientation of the magnetization within the external field range of application. The GMR in these structures is related to the relative angle between the magneti- zation of the two ferromagnetic layers. This can be achieved by taking advantage of magnetic layers with different properties. For example [4], large crystallite sizes can ensure the rigidity of the *Corresponding author. Tel: +33-3-88-10-70-67; fax: +33-3- 88-10-72-49. E-mail address: aziz.dinia@ipcms.u-strasbg.fr (A. Dinia). 0921-4526/02/$-see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0921-4526(02)00518-5