NATIONAL HIGH MAGNETIC FIELD LABORATORY 2006 RESEARCH REPORT TEMPERATURE-AND FIELD-DEPENDENT FAR-INFRARED STUDIES OF LPCMO FILMS N. Margankunte, T.P. Dhakal, D.J. Arenas, A. Biswas, D.B. Tanner (UF, Physics); A. Zimmers (CSR, U., Maryland); Y.J.Wang (NHMFL) Introduction The rare earth manganties, R 1-x A x MnO 3 (where R is a trivalent rare earth ion and A is divalent alkaline-earth ion) have attracted considerable attention in recent years, both because of their versatile physical phenomena and on account of potential device applications. Of special interest are the Insulator to Metal (I-M) transition, charge ordering and colossal magneto resistance (CMR) (a phenomenon where magnetic fields induce large changes in the resistivity). The complex interplay between charge, spin, lattice and orbital degrees of freedom precludes description of these phenomena based only on double exchange. Indeed dynamic Jahn-Teller coupling [1], polaron absorption [2] and phase separation [3] have been put forward as explanatory mechanisms. In this paper, we present field dependent far-infrared measurements of LPCMO thin films. Experimental Thin Films of (La 0.4 Pr 0.6 ) 0.6 Ca 0.33 MnO 3 were grown on LaAlO 3 substrates using pulsed laser deposition. The temperature- dependent measurements were measured at UF using a Bruker 113v equipped with a 4.2K Bolometer for the far-infrared and a HgCdTe (MCT) detector in the mid-infrared. The magnetic field studies were performed at the National High Magnetic Field Laboratory, in the 18T superconducting magnet, using a Bruker 66v spectrometer with custom-built light-pipe optics to carry the far-infrared radiation through the sample and on to a 4.2K helium-cooled bolometer detector [4]. Results and Discussion Temperature dependent measurements (Fig. a) show evidence of phase coexistence as most of the film is still in the insulating state even at 4.2K. Magnetic-field studies (Fig. b) at 12 K (the 4.2 K reflectance spectra have been multiplied with 12 K zero field data) show a metal to insulator transition, seen as large changes in reflectance of the film. The optical conductivity, extracted from standard film fitting procedures is shown in (Fig. c) shows large increase in the Drude part, along with evidence for other charge ordered phases. Fig. a Fig. b Fig. c Conclusions The magneto-optical study has shown multiple phase coexistence in thin films of LPCMO. The nature of the different charge-ordered and ferromagnetic phases in the context of effective medium theories is under investigation. Acknowledgements NM and DBT acknowledge support from the DOE, DE-AI02-03ER46070, and the NSF, DMR-0305043. NHMFL is supported by NSF Cooperative Agreement No. DMR-0084173 and by the State of Florida. References [1]. Millis, A.J ., et al., Phys. Rev. Lett. 77, 175 (1996). [2]. Kaplan, S.G., et al., Phys. Rev. Lett. 77, 2081 (1996). [3]. E. Dagotto et al., Phys. Rep. 344, 1 (2001). [4]. Ng, H.K., et al., Physical Phenomena at High Magnetic Fields-II, Singapore: World Scientific, 1996, pp.~729.