In this study the preparation, magnetic and magnetotransport properties of cobalt-iron pyrite (CO0.5Fe0.5S2) thin films are reported. These materials have been recently proposed as a tunable source of highly spin-polarized electrons. The films have been prepared by thermal-sulfidation Of Co50Fe50 films fabricated by pulsed laser deposition in a sulfur atmosphere at 500 degrees C, at a pressure of 105 Pa for 12 h. The magnetoresistance curves show an extrinsic negative low field part that is related to alignment of the magnetization between neighbouring grains and scales with M-2 as in polycrystalline manganites and it is maximized in thinner films. This is superimposed on a positive, linear high field part. The Hall effect has a strong anomalous contribution typical of ferromagnetic materials. (c) 2007 Elsevier B.V. All rights reserved.