Journal of Magnetism and Magnetic Materials 290–291 (2005) 948–951 Magneto-optical investigation of spin polarisation of La 0:7 Ca 0:3 MnO 3 and La 0:7 Sr 0:3 MnO 3 R. Rauer a, , G. Neuber a , J. Kunze a , J. Ba¨ckstro ¨m a , M. Ru¨bhausen a , T. Walter b , K. Do¨rr b a Institut fu ¨r Angewandte Physik, Universita ¨tHamburg, Jungiusstra X e 9, D-20355 Hamburg, Germany b Institut fu ¨r Festko ¨rper- und Werkstofforschung, D-01171 Dresden, Germany Available online 10 December 2004 Abstract We investigate the ferromagnetic phase of thin epitaxialfilms of the CMR manganitesLa 0:7 Ca 0:3 MnO 3 and La 0:7 Sr 0:3 MnO 3 by temperature-dependent spectralgeneralised magneto-optical ellipsometry (SGME).The phase transitionsfrom a paramagnetic insulator to a ferromagnetic metal take place at T C 265 K and T C 335 K; respectively. The measurements covering a spectral range of0.5–5 eV are performed in the temperature range of 25–425 K. SGME allows a complete magneto-optical characterisation consisting of the determination of the diag components e xx as well as the off-diagonal components e xy of the dielectric tensor within a single measurement. Upon cooling through the Curie temperature, we observe the development of a Drude-like free-carrier response in e xx ; indicating the release of previously bound charges. Meanwhile,e xy exhibits a rising magneto-optical response. This reflects, via the increasing degree of spin polarisation of the bands involved in optical transitions, the emergence of ferromagnetism. We tentatively assign spectral features between 2.5 and 4.5 eV to transitions involving the Mn especially the e g and t 2g levels. r 2004 Elsevier B.V. All rights reserved. PACS: 78.20.Ls; 75.74.Lx Keywords: Magneto-optics; Magnetic oxides; Spin polarization A variety of manganese oxides exhibit the colossal magnetoresistance (CMR) effectin the vicinity ofthe transition from a paramagnetic insulating to a ferro- magnetic metallic phase [1,2]. Recentstudiessuggest that the CMR effect may not be properly explained by a first-order transition between two pure phases but by the coexistence of competing phases [3]. In order to under- stand the influence of phase separation on the physical propertiesof the manganites, it is thus necessary to characterise the involved pure phases. Here,we report on an optical study of theferromagneticphaseof La 0:7 Ca 0:3 MnO 3 (LCMO) and La 0:7 Sr 0:3 MnO 3 (LSMO) by spectralgeneralised magneto-optical ellipsometry (SGME). The optical responseof a solid to an applied electromagnetic field is characterised by its dielectric tensor e: In case of cubic symmetry with the magnetisa- tion ~ M along the~ z direction, e is of the form e ¼ xx xy 0 xy xx 0 0 0 zz 0 B @ 1 C A (1) ARTICLE IN PRESS www.elsevier.com/locate/jmmm 0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.11.297 Corresponding author. Fax: +49 4042838 4368. E-mail address: rauer@physnet.uni-hamburg.de (R. Rauer).