Thin Solid Films, 75 (1981) L15-L16 L15 Letter Magnetic behaviour of thin films of Co-Pt alloys with 33 at. ~ Co and 60 at. % Co V. GEORGESCU AND V. TUTOVAN Electrical Laboratory, "ALL Cuza" University,Jassy (Romania) (Received October 27, 1980; accepted November 12, 1980) 1. Introduction Following our study on the magnetic behaviour of Co-Pt electrolytic thin films1, in this paper we consider some of these films with a non-stoichiometric composition. Our aim is to contribute to the understanding of the composition dependence "of the magnetic characteristics of Co-Pt films. We chose films containing approximately 33 at.% Co and 60 at.% Co (the error being 0.2%) since the magnetic characteristics of these films differ most from those with the stoichiometric compositions CoPt3, CoPt and Co3Pt. The method of preparing the samples and the experimental procedure have been described elsewhere 1. Films 50-500 nm thick were deposited onto copper discs of diameter 19.5 mm and thickness 0.5 mm. 2. Experimental results The variations of the saturation magnetic induction Bs and the coercive field H c with thickness for these films are less marked than those for films with a stoichiometric composition. The behaviour of Co-Pt films with non-stoichiometric composition is also different from that of films with stoichiometric composition as far as both the form of the hysteresis cycle (Fig. 1) and the energy loss due to rotational hysteresis (Fig. 2) are concerned. The curves showing the variation of the saturation magnetization with the temperature indicate the presence within the sample of two phases with different Curie temperatures: T 1 = 390 K and T 2 = 768 K for the films with 33 at.% Co; T 1 = 773 K and T2 = 1071 K for the films with 60 at.% Co. The experimental results show that the films studied consist of two phases with different ferromagnetic characteristics. 3. Discussion Some papers dealing with bulk samples support our statement. It is known that alloys of the Cu-Au type with stoichiometric composition are ordered and form the L 10 or L 12 superstructures. In contrast, alloys of the same type but having a non-stoichiometric 0040-6090/81/0000-0000/$02.50 © Elsevier Sequoia/Printed in the Netherlands