DOI: 10.1007/s00339-005-3424-9 Appl. Phys. A 82, 697–701 (2006) Materials Science & Processing Applied Physics A r. ranchal 1, ✉ c. aroca 2 m.c. s ´ anchez 1 p. s ´ anchez 2 e. l ´ opez 1 Improvement of the structural and magnetic properties of Permalloy/Gadolinium multilayers with Mo spacers 1 Dept. F´ ısica de Materiales, Facultad de C.C. F´ ısicas, Universidad Complutense de Madrid, Ciudad Universitaria s/n 28040 Madrid, Spain 2 ISOM & Dpt. F´ ısica Aplicada, E.T.S.I. Telecomunicaci´ on, U.P.M. 28040 Madrid, Spain Received: 20 June 2005/Accepted: 22 September 2005 Published online: 24 November 2005 • © Springer-Verlag 2005 ABSTRACT We have studied the influence of the growth condi- tions on the structural characteristics of sputtered Py(Fe 20 Ni 80 )/ Gd/Py(Fe 20 Ni 80 ) thin films. Auger electron spectroscopy re- veals the existence of Ni in the Gd layer. The Ni concentration profile appears asymmetric with a higher concentration close to the top Py layer. This asymmetrical Ni concentration produces a different coercivity of each Py layer. It is possible to reduce the Ni interdiffusion by using multilayers based on Py/Gd bilayers separated by Mo spacers between the Py/Gd bilayers. In these samples we have obtained an enhancement of the structural and magnetic properties. PACS 81.15.Cd; 66.30.-h 1 Introduction Multilayers of transition magnetic metals (TM) and Gadolinium (Gd) attract interest due to the antiferromag- netic coupling between the TM and Gd magnetic moments. However, these multilayers exhibit a very different magnetic behavior when the temperature decreases because of the high Gd Curie temperature (293 K) compared to other heavy rare earths. Theoretical [1–3] and experimental work [4–7] have shown that this antiferromagnetic coupling in the interfaces of TM/Gd multilayers can create different magnetic structures, like an in-plane domain wall (DW) parallel to the surface, due to the competition between exchange and Zeeman energies. Ferrimagnetic structures with an extensive number of mag- netic configurations have been reported in thin films of GdCo alloys due to this kind of coupling [8, 9]. Moreover, positive exchange-bias has been observed in ferro/ferrimagnetic bi- layers of FeSn/FeGd [10] due to a DW located at the interface. In CoNi/Gd trilayers and bilayers it has been found that the exchange-bias sign depends on the Gd thickness [11] proba- bly due to the existence of a DW at the interface. Multilayers comprising Co layers have shown a composi- tion gradient due to the strong interdiffusion of Co in Gd [12]. CoNi/Gd bilayers show that the deposition order influences ✉ Fax: +(34) 91 394 45 47, E-mail: rociran@fis.ucm.es on the coercivity are also due to the interdiffusion [13]. There- fore, as the interdiffusion affects the magnetic behavior and the transport properties of these multilayers [12, 14, 15], a pre- vious improvement of their structural characteristics is recom- mended to obtain reliable magnetic and electrical properties. Studies of TM/Gd have been carried out by using mainly Fe, Co, and their magnetic alloys as the TM [4–9, 11–16], but the high coercivity of Fe and Co makes these multilay- ers inappropriate for some applications and thus the study of multilayers of Gd and soft magnetic alloys is necessary. In this work, the structural characteristics of Py(Fe 20 Ni 80 )/ Gd/Py trilayers have been studied as a function of growth conditions. An asymmetrical Ni diffusion appears in the Gd layer which affects the magnetic properties of the trilayers, the Gd layer magnetization is reduced by the Ni diffusion and only a weak Py–Gd exchange coupling appears. Multilayers grown at low deposition power based on Py/Gd bilayers sep- arated by Mo spacers, have been proposed as a solution. In these samples the exchange coupling is enhanced and the Gd magnetization is important in the magnetization process. 2 Experimental Samples were grown in a dc-magnetron sputtering system on corning-glass substrates as explained in [17]. The system allows substrate rotation during the growth, and the application of an in-plane magnetic field. Depositions were done at room temperature in a chamber with an initial pressure under 4 × 10 −7 mbar being the Ar pressure 2 × 10 −3 mbar in all cases. Deposition power of 30 and 50 W were used for Py/Gd/Py trilayers while bilayers and multilayers were only grown at 30 W. Single layers of Gd were evaporated at differ- ent powers for additional comparisons. Mo layers of 10 nm, 20 nm and 60 nm have been used as buffer, spacer and cap- ping layers. The first set of Py/Gd/Py trilayers where grown without rotating the substrates. In all the other samples, sub- strates were rotating during the growth in order to improve the homogeneity. High-angle diffraction Θ − 2Θ scans and low-angle X-ray reflectivity were used for structural characterization. An atomic force microscope (AFM) microscope (Vecco Metrol- ogy) working in tapping mode was used for the study of the interface morphologies. Composition depth profiles were carried out by using auger electron spectroscopy (5 keV) com-