Journal of Magnetism and Magnetic Materials 280 (2004) 322–326 Magnetoresistance of Fe 3 O 4 /Au/Fe 3 O 4 and Fe 3 O 4 /Au/Fe spin-valve structures Sebastiaan van Dijken*, Xavier Fain, Steven M. Watts, Kentaro Nakajima, J.M.D. Coey SFI Trinity Nanoscience Laboratory, Physics Department, Trinity College, Dublin 2, Ireland Received 14 January 2004; received in revised form 9 March 2004 Abstract A detailed study of the in-plane magnetotransport properties of spin valves with one and two Fe 3 O 4 electrodes is presented. Fe 3 O 4 /Au/Fe 3 O 4 spin valves exhibit a clear anisotropic magnetoresistance in small magnetic fields but no giant magnetoresistance (GMR). The absence of GMR in these structures is due to simultaneous magnetization reversal in the two Fe 3 O 4 layers. By contrast, a negative GMR effect is measured on Fe 3 O 4 /Au/Fe spin valves. The negative GMR is attributed to an electron spin scattering asymmetry at the Fe 3 O 4 /Au interface or an induced spin scattering asymmetry in the Au interfacial layers. r 2004 Elsevier B.V. All rights reserved. PACS: 75.70.Cn; 73.50.h; 75.70.i Keywords: Magnetite; Magnetoresistance; Magnetic spin valve 1. Introduction Thin films of Fe 3 O 4 are of great interest for spin- dependent transport devices since they combine a large negative spin polarization with a high Curie temperature of 858 K. Although experiments have not confirmed the predicted complete half-metalli- city of Fe 3 O 4 , they do show that the number of minority electrons is much larger than the number of majority electrons at the Fermi level [1,2]. The incorporation of Fe 3 O 4 films in magnetic tunnel junctions or spin valves is therefore expected to yield large magnetoresistance (MR) values that, depending on the counter electrode, can be either positive or negative. Recent transport measure- ments on magnetic tunnel junctions do indeed demonstrate the potential of Fe 3 O 4 for spintronic applications [3,4]. In this paper, we report on the MR of Fe 3 O 4 /Au/Fe 3 O 4 and Fe 3 O 4 /Au/Fe spin- valve structures in the current-in-plane geometry. 2. Experimental procedure The spin valves were grown by dc-magnetron sputtering on MgO(0 0 1) substrates in a Leybold Z550-S system with a base pressure of 10 7 mbar. The magnetite layers were reactively sputtered ARTICLE IN PRESS *Corresponding author. Tel.: +35316083034; fax: +35316083037. E-mail address: vandijks@tcd.de (S. van Dijken). 0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.03.030