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ABSTRACT Microstructural and

magnetoresistance properties of La0.6Y0.07Ca0.33MnOx (Y-doped

LCMO) thin films grown in-situ by pulsed laser ablation have been studied. Transmission electron microscopy and x-ray diffraction measurements have shown that the Y-doped LCMO thin films grow epitaxially on (100) LaA103 substrates and are cubic with a lattice parameter of 3.849 A. The as-deposited films exhibited a metal-insulator transition at 130 K and a giant magnetoresistance (GMR) at 125 K with a MR ratio (dR/RH) of 1500% in the presence of a magnetic field of 6 Tesla. Such a colossal value of MR ratio for as-deposited Y-doped LCMO films is quite promising keeping in view the fact that these fidms were unannealed and not optimized. We ascribe this magnetoresistance to spin-dependent electron scattering coupled with the presence of intervening 02. ions across Mn3" and Mn4" with suppressed separation between Mn-O layers caused by smaller sized Y-dopant. The effect of annealing on the positive-shift of metal-insulator transition temperature and the improvement in GMR ratio has also been discussed. We also report a nonohmic response in the Y-doped LCMO films which is observed only in the region of the resistance peak and lends support to a conduction mechanism in these materials based on spin-dependent scattering of electrons, INTRODUCTION The ability of a magnetic field to alter the scattering of conduction electrons and thereby to govern the flow of electrical charge in a material is a well known phenomenon. In fact, the change in electrical resistance in response to a magnetic field, known as magnetoresistance (MR), has acquired a significant technological importance over the last several years as it makes possible to read information in a magnetic medium, such as a computer hard disk. The recent observation of colossal magnetoresistance in generated further

some Perovskite-structured lanthanum manganites 1-15 has The advantage of lanthanum manganites over the

interest in this field.

241 Mat. Res. Soc. Symp. Proc. Vol. 397 01996 Materials Research Society

conventional metallic multilayered structures 16-20 lies in their larger MR ratios. It is this large difference ( one to three orders of magnitude) in the MR ratio which has culminated into addition of an adjective 'giant' before the word magnetoresistance making the effect commonly known as giant magnetoresistance (GMR) effect. The phenomenon of GMR is potentially of great interest because it offers the possibility of a large increase in output voltage of a MR sensor. In this letter, we report our studies on the growth, structural characterization and giant magnetoresistance effect in Y-doped LCMO thin films. We also present the beneficial effect of annealing for the realization of Y-doped LCMO films, not only with larger magnetoresistance value but also with higher metal-insulator (M-1) transition temperature. EXPERIMENT The bulk target of La0.6Y0.07Ca0.3MnOx of nominal composition was prepared using a ceramic processing route 22,23. The component oxides of La a