Journal of Magnetism and Magnetic Materials 313 (2007) 142–150 Magnetic properties and structure of FePt/FeMn multilayers Nguyen N. Phuoc à , Takao Suzuki Information Storage Materials Laboratory, Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511, Japan Received 13 October 2006 Available online 3 January 2007 Abstract A systematic study of the magnetic properties by ion beam sputter-deposition system, was conducted in conjunction with the structure of FePt/FeMn multilayers fabricated onto MgO(0 0 1) substrates. Both parallel and perpendicular exchange biases were observed in the multilayers and were found to decrease drastically, as the deposition temperature is higher than 350 1C, which is evidently due to the interdiffusion at the interface. The thickness dependence study shows that the perpendicular magnetic anisotropy observed in the multilayers originates from surface anisotropy, being consistent with the decrease of perpendicular magnetic anisotropy as the deposition temperature is increased. The difference between parallel and perpendicular blocking temperatures that was clearly observed, is possibly due to the spin canting out of plane at the interface. r 2007 Elsevier B.V. All rights reserved. PACS: 75.70.Cn; 75.70.i; 75.25.+z; 75.30.Gw Keywords: Perpendicular exchange bias; Surface anisotropy; Magnetic thin film; Multilayer 1. Introduction Exchange bias between ferromagnet (FM) and antiferro- magnet (AF) discovered in 1956 by Meiklejohn and Bean [1] has been extensively studied due to its potential applications in spin-electronics devices [2]. It is so named because the phenomenon manifests itself in a shift of the hysteresis loop after field-cooling samples through the Ne´ el point. Although there have been numerous studies on this phenomenon, its physical origin is still under debate. Almost all the studies so far on this subject were carried out in the so-called parallel configuration, i.e. samples were field cooled with the external field applied in the film plane. Recently, several groups have shown that perpendicular exchange bias can be established in multilayers [3–11]. However, there is still a lack of systematic studies on perpendicular exchange bias in comparison with parallel exchange bias to clarify the mechanism of perpendicular exchange bias. Therefore, the purpose of the present work is to study exchange bias in both parallel and perpendicular directions in conjunction with structural properties of FePt/FeMn multilayers. In particular, the investigation of parallel and perpendicular exchange biases, as well as of perpendicular magnetic anisotropy dependent on deposition temperature and FePt thickness, is performed. 2. Experimental Samples with stacks of [FePt/FeMn] 10 with various thicknesses of FePt layers were fabricated onto MgO(0 0 1) substrates using ion beam sputter-deposition system with the base pressure better than 2  10 6 Pa. The substrate temperature during deposition was held at various temperatures from 25 to 550 1C. No external field was applied during deposition. A capping layer of Ru (3 nm thick) was deposited in order to protect FeMn layer from oxidation. The deposition rates are 0.27 and 0.34 A ˚ /s for FePt and FeMn layers, respectively. The composition of FeMn and FePt films, analyzed by energy dispersive X-ray spectroscope (EDS), are 43:57 and 44:56, respectively. X-ray diffraction technique was used to characterize ARTICLE IN PRESS www.elsevier.com/locate/jmmm 0304-8853/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.12.016 à Corresponding author. Tel.: +052 809 1872; fax: +052 809 1874. E-mail addresses: phuoc@toyota-ti.ac.jp, nnguyenphuoc@yahoo.com (N.N. Phuoc).