Magnetic reversal of ion beam patterned Co/Pt multilayers Greg J. Kusinski a,b,c, * , Kannan M. Krishnan c,d , Gregory Denbeaux c , Gareth Thomas a,b,c a MMFX Technologies, R&D, 2 Corporate Park Suite 102 R&D, Irvine, CA 92606, USA b Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, USA c Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA d Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA Received 1 August 2002; received in revised form 24 September 2002; accepted 25 September 2002 Abstract The characteristics of the reversal processes of magnetic arrays fabricated by ion-irradiation of Co/Pt multilayers with perpendicular magnetic anisotropy are reported. Magnetic patterns with periodicities from 1 lmto100nmwere patterned. A correlation between the pattern size, magnetic reversal and grain size is presented. Ó 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved. Keywords: Multilayers; Magnetic imaging; Magnetic domains; Transmission X-ray microscopy; Transmission electron microscopy 1. Introduction and background In order to sustain the growth of magnetic re- cording, the limitations associated with super- paramagnetic grains must be solved [1]. The new approach to ultrahigh-density magnetic storage, is based on patterning of perpendicular magnetic media into individual single domain elements [2]. A specific example is the Co/Pt multilayer (ML) structure with perpendicular magnetic anisotropy (PMA), where the PMA can be systematically re- duced by ion irradiation [3–5]. In this paper the characteristics of the reversal processes of magnetic arrays fabricated by ion- irradiationofCo/Ptmultilayers(MLs)arereported. TheMLs {20nmPtseed/10(0.3nmCo/1nmPt)/1 nm Pt cap layer} with perpendicular anisotropy weredepositedbyelectronbeamevaporationonto electron transparent Si 3 N 4 windows. Previously the effects of growth temperature and ion-irradia- tion on the microstructure and the magnetic do- mainstructurewereinvestigated[5–8].Itisknown that with an increasing dose of ion irradiation the perpendicular coercivity H C of the Co/Pt MLs decreases without affecting the square loop shape. With further increase in the irradiation dose, the transition from out-of-plane to in-plane easy magnetization axis is obtained. This ability to control and vary the magnetic property by ion-ir- radiation, makes Co/Pt MLs very attractive for patterned media applications [9–11]. Scripta Materialia 48 (2003) 949–954 www.actamat-journals.com * Corresponding author. Present address: MMFX Technol- ogies, R&D, 2 Corporate Park Suite 102 R&D, Irvine, CA 92606, USA. Tel.: +1-9494767600; fax: +1-9494741130. E-mail address: kusinski@calalum.org (G.J. Kusinski). 1359-6462/03/$ - see front matter Ó 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved. doi:10.1016/S1359-6462(02)00607-3