Ž . Thin Solid Films 380 2000 211214 Giant magnetoresistance increase in a hard  soft spin valve structure with the growth of a semiconductor layer M. Guth  , S. Colis, G. Schmerber, A. Dinia ( ) IPCMS-GEMME UMR 7504 du CNRS , ULP-ECPM, 23 rue du Loess, F-67037 Strasbourg, France Abstract Magnetic and transport properties of a hard  soft spin valve structures have been investigated. A first series of sandwiches Ž . composed of an artificial antiferromagnetic AAF CoRuCo sandwich decoupled from a soft FeCo buffer layer as follows: Fe Co Cu Co Ru Co Cu Cr has been prepared. This sandwich presents a giant magnetoresis- ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ 50 A 5A 30 A 30 A 5A 30 A 20 A 20 A Ž . 2 tance GMR of 1.7% and an exchange coupling strength of approximately 1.73 ergcm . Afterwards, we have grown a second ˚ series of sandwiches in which the CuCr capping layer has been replaced by a 15-A thin semiconductor layer of ZnS, covered by a soft ferromagnetic layer of Co Fe . Surprisingly, the giant magnetoresistance for the last sandwiches has been increased ˚ ˚ 5A 50 A by a factor of 2, up to 4%. To explain this non-expected result, we have performed atomic force microscope imaging at the semiconductor layer surface. The results show that the semiconductor layer is not homogeneous and contains a non-negligible ˚ density of pin-holes, that are responsible of a direct magnetic coupling between the upper 30 A Co layer of the AAF and the Co 5 ˚ ˚ AFe 50 A bilayer. This coupling induces a strong asymmetry between the magnetic layers of the AAF and consequently an enhancement of the GMR.  2000 Elsevier Science B.V. All rights reserved. Keywords: Magnetoresistance; Spin-valve; ZnS; Artificial antiferromagnet  Since its discovery 1, giant magnetoresistance Ž . GMR has remained at the center of an important part of current research in magnetism. This is partly due to its importance as a fundamental phenomenon as  well as to its potential for applications 2 . Although many studies have already been done on the CoRuCo sandwiches, and some interesting charac- teristics have already been reported for the CoRu   thin films 3  7 , this system is still interesting and allows to observe some new features. Recently, Colis et  al. 8 have experimentally demonstrated the influence of the nature and of the quality of the buffer layer on the transport and magnetic properties of CoRuCo Ž . trilayers deposited by ion beam sputtering IBS on glass substrates. The best result has been obtained with the following structure: Fe Co Cu Co  ˚ ˚ ˚ ˚ 50 A 5A 30 A 30 A Ru Co Cu Cr with a GMR value of ˚ ˚ ˚ ˚ 5 A 30 A 20 A 20 A  Corresponding author. approximately 1.7% and a coupling strength reaching J 1.7 ergcm 2 . This stack is similar to a classical AF spin valve structure in which the artificial antiferromag- netic CoRuCo sandwich corresponds to a hard layer, which is decoupled from the FeCo soft layer by a 30 ˚ A Cu non-magnetic layer. In this structure the GMR signal is the result of two additional contributions: the first contribution to the GMR is due to the AAF trilayer, while the second contribution is the result of the interaction between the AAF and the magnetic soft buffer layer. Since the above spin valve structure has been already optimized in terms of antiferromagnetic coupling and GMR, the aim of this paper is to use the same spin  valve structure as Colis 8 , and to cover the second Co ˚ layer of the AAF sandwich with a 15-A ZnS semicon- ductor layer, followed by the growth of a second soft ˚ ˚ ferromagnetic detection layer of Co 5 AFe 50 A. The role of the semiconductor layer is to electrically isolate the AAF sandwich from the second CoFe detection 0040-609000$ - see front matter  2000 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 4 0 - 6 0 9 0 00 01507-8