Journal of Magnetism and Magnetic Materials 72 (1988) 279-284 279 North-Holland, Amsterdam SURFACE INDUCED MAGNETIC AND MAGNETO-OPTICAL PROPERTIES IN AMORPHOUS COxY l_ x THIN FILMS J.M. ALAMEDA, M.C. CONTRERAS Dpto. de Fisica, Facultad de Ciencias, Universidad de Oviedo, 33007 Oviedo, Spain and A.R. LAGUNAS Inst. Ciencias de los Materiales, CSIC, Serrano 144, 28006 Madrid, Spain Received 8 June 1987; in revised form 30 December 1987 Room temperature magneto-optical spectroscopy (transverse Kerr effect) (MOKE) and transverse biased initial susceptibil- ity (TBIS) measurements have been carried out in amorphous Co~,Y1_ x thin films (thickness: 1000 ~,). The chemical composition range studied was 0.50 ~< x ~< 0.80. The MOKE, TBIS and coercive force show a marked dependence on x. For x > 0.65 the MOKE parameter 8 k is positive and TBIS behaviour leads to a magnetization ripple contribution to the effective field. When x < 0.60, 8 k is negative and TBIS behaviour may be explained by a cluster model of non-interacting magnetically ordered regions and ,'andom distribution of associated anisotropies. At x = 0.65, two magnetic phases become apparent from MOKE a TBIS beh:'.viour. These facts are explained by the occurrence of sublayer Co-enriched regions induced by surface segregation of Y. Optical effects in protective Y-oxide layers may be at the origin of the change in Kerr effect polarity. 1. Introduction Magnetic and magneto-optical properties of thin films of Rare Earth-Transition Metal (RE-TM) alloys, have been widely studied be- cause of their magneto-optical storage media ap- plications [1]. For a better understanding of many of the observed effects, which includes surface or interface properties [2], it will be interesting to analyze the magnetic and magneto-optical contri- bution arising from the 3d magnetic sublattice alone. We have chosen amorphous COxYl_x al- loys, where Co moment determination [3,4], NMR [5] and FMR [6,7] studies have been already re- ported. Room temperature magnetic properties of strong magnetic alloys (x > 0.65), analized by transverse biased initial susceptibilyty (TBIS) [8], have been already reported [9]. This report con- cerns mainly to the room temperature magnetic and magneto-optical properties of samples which are weakly magnetic alloys at 4.2 K. (i.e. 0.50 < x < 0.65). 2. Experimental Amorphous CoxYl_z films (thickness 1000 ,~) were grown on glass substrates maintained at room temperature. We use a special dc assisted triode- sputtering system [10] (Ar pressure=4x 10 -4 Torr) where simultaneous codeposition from two independently polarized Y and Co cathodes is available. By means of a precalibration of the sputtering rate of both cathodes versus voltage, the ratio between Y and Co was prefixed to obtain five different values of relative concentrations within the range 0.50 < x ~< 0.80. Subsequent chemical composition determination by Induc- tively Coupled Plasma Atomic Emission Spec- trometry (ICP-AES) was utilized in several films 0304-8853/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)