Journal of Magnetism and Magnetic Materials 304 (2006) e303–e305 Optical and magneto-optical studies of (La 0.7 A 0.3 )MnO 3 (A ¼ Sr, Ca, and Ce) thin films H.L. Liu a,Ã , Kenneth Y.-J. Zhang a , L.C. Wu a , L. Uba b , S. Uba b , W.J. Chang c , J.-Y. Lin c , L.M. Wang d a Department of Physics, National Taiwan Normal University, Taipei, Taiwan b Institute of Experimental Physics, University of Bialystok, Bialystok, Poland c Institute of Physics, National Chiao Tung University, Hsinchu, Taiwan d Department of Electrical Engineering, Da-Yeh University, Changhua, Taiwan Available online 6 March 2006 Abstract The optical and magneto-optical (MO) properties of (La 0.7 A 0.3 )MnO 3 (A ¼ Sr, Ca, and Ce) thin films have been investigated. It is found that the value shape of spectra is strongly dependent on different cation dopings. The Sr-doped thin film exhibits a strong Drude response and maximum Kerr rotation angle of 0.321 at 3.4 eV. Interestingly, the replacement of Sr ions with the smaller Ca ions and the tetravalent Ce ions all lead to a remarkable suppression of the carrier density and the MO response. Such differences are interpreted as due to their different electronic band structures. r 2006 Elsevier B.V. All rights reserved. PACS: 74.25.Gz; 75.47.Gk; 78.20.Ls Keywords: Colossal magneto-resistance; Optical property; Magneto-optical effect 1. Introduction The subject of colossal magneto-resistance (CMR) effect in the manganite thin films R 1x A x MnO 3 (R and A being trivalent rare-earth and divalent alkaline-earth ions, respectively) continues to attract much attention [1,2]. Interest in these systems is exemplified by their potential technological applications related to magnetism and spintronics. The films often have different CMR effects and Curie temperatures (T C ) compared to bulk materials due to lattice mismatch between the film and the substrate. In this study, we further show that the optical and magneto-optical (MO) properties of the manganite thin films are critically dependent on different cation dopings such as Sr, Ca, and Ce. To the best of our knowledge, few studies of the MO properties of the manganites have been reported in the past [3–5]. Our investigations are therefore very important to understand the optical and MO Kerr effects of devices based on the manganite thin films. 2. Results and discussion Thin films of La 0.7 Sr 0.3 MnO 3 (LSrMO), La 0.7 Ca 0.3 MnO 3 (LCaMO), and La 0.7 Ce 0.3 MnO 3 (LCeMO) were grown on (1 0 0) SrTiO 3 substrates using the pulsed-laser deposition or the off-axis magneton sputtering technique described previously [6,7]. The thickness of the films is around 300 nm. The strain effect due to lattice mismatch between the film and the substrate is fully relaxed [8]. Characteriza- tions of X-ray diffraction, DC resistivity, and magnetiza- tion were also preformed on these samples. Fig. 1 shows the temperature dependence of in-plane magnetization under 100 G for the three films, clearly revealing that they have a ferromagnetic transition. The T C for LSrMO is 350 K, whereas that of LCaMO and LCeMO is 275 K. The near-normal optical reflectance spectra of the three films were taken over a wide frequency range (50–55000 cm 1 ) and at temperatures between 20 and ARTICLE IN PRESS www.elsevier.com/locate/jmmm 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.02.074 Ã Corresponding author. Tel.: +886 2 29343163; fax: +886 2 29326408. E-mail address: hliu@phy.ntnu.edu.tw (H.L. Liu).