PREPARATION AND MAGNETORESISTANCE OF LANTHANUM MANGANITES AND SILVER CHALCOGENIDE THIN FILMS Klaus-H. Dahmen, Ilya S. Chuprakov, Ed S. Gillman and M. Ming Li, Department of Chemistry and MARTECH, Florida State University, Tallahassee, FL 32306 Abstract The effect of texture and orientation on the resistance (OT and 6T) and magnetoresistance (MR) of Lal-xCaxMnO3 (LCMO) and Ag2Te thin films on various substrates has been investigated. Similar features were found in the MR dependence of thin films of these compounds despite the fact that they belong to different types of MR materials. Epitaxial or strongly oriented films exhibit a peaked MR behavior while for polycrystalline films this curve does not have sharp features. Sign reversal effect of MR was found also in thin films of Ag2Te. MR changes from positive at transverse field-,eurrent orientation to negative at parallel orientation. Introduction The antiferromagnetic perovskite oxide lanthanum manganite (LaMnO3) shows both metallic conduction and ferromagnetism when trivalent La+ 3 ions are partially substituted with divalent cations. Divalent Doping of Lal-xMxMnO3 with 0.20 < x < 0.50 and M2+ = Ca, Ba, Sr ,Pb , Cd results in the formation of mobile charge carriers and ferromagnetic order with some canting of the Mn spins. The observation of a colossal magnetoresistance (CMR) in this doping range at temperatures near the ferromagnetic-paramagnetic ordering supports a strong correlation between the transport and magnetic properties in these materials. High temperature MR have been found predominantly of Lal-xMxMnO3 films which were deposited highly oriented or even epitaxially, onto single crystalline substrates such as LaAlO3 (LAO), MgO. Low temperature MR has recently been observed in both Sr and Ca doped polycrystalline manganites [1,2]. In both cases the temperature dependence of the MR runs trough a maxima. In these experiments the low temperature MR is explained in terms of disorder-induced canting of the Mn spins in the grain boundary region and spin-polarized tunneling at the grain boundaries. Large positive magnetoresistance (MR) effect was recently discovered in nonmagnetic silver chalcogenides, Ag2Se and Ag2Te [3]. These materials have outstanding properties such as magnetoresistance (MR) values up to 200% at room temperature at 4T, linear field dependence of MR down to 100 Oe, almost flat temperature dependencies of MR at room temperature, and low resistance in the range of milliohms-cm. Recently we confirmed this effect in thin films of these materials [4]. These compounds belong to the class of narrow band-gap semiconductors but grain boundary effect can also play an important role in this type of MR materials. Experimental part Lal-xCaxMnO3 films LCMO thin films with x = 0.41 were prepared on LAO(001), LAO(Oll), YSZ(00I) and SAP(0001) single crystal substrates by liquid delivery metallo-organic chemical vapor deposition (LD-MOCVD) as follows. An NZ-Applied Technologies liquid delivery vaporization system was used to deliver the 2,2,6,6-tetramethyl-3,5-heptanedionato (TMHD) organometallic precursors; La(TMHD)3, Mn(TMHD)3, and Ca(TMHD)2 which were dissolved in 25 ml of 39 Mat. Res. Soc. Symp. Proc. Vol. 547 © 1999 Materials Research Society