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MATERIALS RESEARCH

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Screen printed La2/3 Sr1/3 MnO3 thick films on alumina substrates L. Durand, Ll. Balcells, A. Calleja, J. Fontcuberta, and X. Obradors Institut de Ci`encia de Materials de Barcelona (CSIC), Campus Universitat Aut`onoma de Barcelona, E-08193 Bellaterra, Catalunya, Spain (Received 28 July 1997; accepted 9 January 1998)

We report here on the preparation of La2/3 Sr1/3 MnO3 magnetoresistive thick films on polycrystalline Al2 O3 substates by using the screen printing technique. It is shown that films can be obtained using high temperature sintering. While there is a reacted layer, this improves adhesion and is not too troublesome if the films are made thick enough. It is shown that PbO–B2 O3 –SiO2 glass additives allow sintering at lower temperatures and can be used to improve the mechanical stress of the films. However, it is found that glass concentrations large enough to significantly improve the film adherence result in a weak low field magnetoresistance probably because grains are coated with high resistivity material. Strategies to overcome these difficulties are discussed.

I. INTRODUCTION

Magnetoresistive materials based on manganese perovskites of L12x Ax MnO3 type, where L is a lanthanide and A is a divalent alkaline-earth are currently being intensively studied.1 Aside from its scientific interest related to their rich physical properties, the expectation of useful materials for technological applications promotes research on materials of enhanced field sensitivity and in a form suitable for device fabrication. The discovery that grain boundaries and interfaces2–4 can be important sources of low-field magnetoresistance (LFMR) has stimulated renewed interest on ceramic or granular L2/3 A1/3 MnO3 oxides. Tailoring of artificial interfaces by using appropriate substrates and epitaxial thin film technologies is being initiated.5 In brief, it appears that magnetic scattering or tunneling of polarized charge carriers across interfaces is extremely sensitive to applied magnetic fields. Therefore, the current issue is to understand and modify the nature of interfaces and the magnetic coupling across them. Two different strategies have so far been reported: the modification of the magnetic surface frustration of grains by appropriate tailoring of the intragrain magnetic interaction strength4 and the change of the magnetic coupling through interfaces by changing the grain boundary angles.5 However, even if the LFMR could be optimized, to get a chance for technological applications, L2/3 A1/3 MnO3 materials still face the problem of development of a suitable low cost technique for film fabrication. The screen printing technique appears to be appropriate; it can be scaled up easily, and it is widely used in fabrication of solid state devices and sensors in industrial environments. Rather preliminary results concerning the use of the screen printing technique to grow thick films of L2/3 A1/3 MnO3 have been recently reported.6 J. Mater. Res., Vol. 13, No. 9, Sep 1998

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