* Corresponding author. Institute of Molecular Physics, Pol- ish Academy of Sciences, PL-60-179 Poznan H , M. Smoluchow- skiego 17, Poland. Tel.: #48-48-612334; fax: #48(61)-86-84- 524. E-mail address: lucinski@ifmpan.poznan.pl (T. Lucin H ski). Journal of Magnetism and Magnetic Materials 222 (2000) 327}336 Growth and properties of Co/Al}O  /Ni(80)Fe(20) trilayers monitored in-situ during deposition process T. Lucin H ski*, S. Czerkas, H. Bru K ckl, G. Reiss Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, PL-60-179 Poznan & , Poland Faculty of Physics, University of Bielefeld, D-33501 Bielefeld, Universita ( tsstrasse 25, Germany Received 30 June 2000 Abstract The Co(25 nm)/Al(d  )}O  /Ni  Fe  (25 nm), trilayers, with a Al thickness variation of 0.5 nm)d  )5 nm, were evaporated in ultra-high vacuum onto oxidised Si wafers. The simultaneous measurements of the magnetic hysteresis loops and thickness-dependent electric conductance were performed in-situ during deposition process. They were supplemented with surface topography and cross section images by atomic force microscopy and high-resolution transmission electron microscopy, respectively. We have shown that for an Al thickness of about 1.2 nm a transition from strongly ferromagnetically coupled Co and Ni  Fe  characterised with single hysteresis loops to well separated magnetisation loops evident for weakly coupled layers occurs. The conductance measurements performed during deposition process as well as during 24 h oxidation process of the Al layer led us to the conclusion that independently on Al thickness nominally only 0.5 nm thick Al layer is oxidised. The in#uence of di!erent bu!er layers (Cu, Au) on magnetisation reversal characteristics is also shown.  2000 Elsevier Science B.V. All rights reserved. Keywords: Ferromagnetic thin "lms; Magnetisation processes; In-situ conductance measurements; Thin "lm growth; Atomic force microscopy. 1. Introduction The large tunneling magnetoresistance (TMR) observed recently in magnetic tunnel junctions composed of ferromagnet}insulator}ferromagnet structures at room temperature (see for instance [1}3]) has great application potential in the digital storage industry [4]. The resistance of such systems depends on the relative orientation of the mag- netisation in the two ferromagnetic layers being maximum for their antiparallel alignment and minimum for parallel magnetisation orientations. [5]. According to the models of Julliere [5] and Slonczewski [6] the magnitude of TMR e!ect is expected to be dependent on the conduction elec- tron spin polarisation of the ferromagnetic elec- trodes. However, for the given ferromagnetic and insulating layers the TMR signal and junction res- istance depend critically on the insulating layer quality, bottom electrode roughness, etc., thus on the thin-"lm deposition conditions (sputtering, evaporation) and on oxidation methods. The most 0304-8853/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 5 6 4 - 3