Magnetic properties of the TiO 2 -Co 3 O 4 system A. Serrano 1 , E. Fernandez Pinel 1,2 , A. Quesada 2,3 , I. Lorite 4 , M. Plaza 1 , L. Pérez 1 , F. Jiménez-Villacorta 5 , J. de la Venta 1 , M. S. Martín-González 6 , J. L. Costa-Krämer 6 , J. F. Fernandez 4 , J. Llopis 1 , M. A. García 1,4* . 1 Dpto. Física de Materiales Universidad Complutense de Madrid, Madrid, Spain 2 Instituto de Magnetismo Aplicado UCM, Las Rozas, Madrid, Spain. 3 Instituto de Ciencia de Materiales de Madrid, CSIC, Madrid, Spain 4 Instituto de Cerámica y Vidrio, CSIC, Madrid, Spain 5 SpLine, Spanish CRG beamline at the ESRF, Grenoble, France and Instituto de Ciencia de Materiales, CSIC, Madrid,Spain. 6 Instituto de Microelectrónica de Madrid, CSIC, Tres Cantos, Madrid, Spain *Corresponding author: email: ma.garcia@fis.ucm.es Abstract We report here the observation of ferromagnetism (FM) at 300 K in mixtures of TiO 2 and Co 3 O 4 powders despite the antiferromagnetic and diamagnetic character of both oxides respectively. The ferromagnetic behavior is found in the early stages of reaction and only for TiO 2 in anatase structure; no FM is found for identical samples prepared with rutile-TiO 2 . Optical spectroscopy and X-ray absorption spectra confirm a surface reduction of octahedral Co +3 →Co +2 in the mixtures which is in the origin of the observed magnetism. 1/15