Influence of grain size on magnetoresistance properties of bulk La0.67Ca0.33MnO3-delta

The magnetic and magnetoresistive properties of six polycrystalline bulk sa mples of nominal chemical composition La0.67Ca0.33MnO3-delta and varying gr ain size(3.3 mu m-20.4 mu m), were investigated. Although the Curie tempera ture, T-c, is independent of grain size, the variation of the saturation ma gnetisation with grain size depends on the magnetic history. At 20 K and 8 T applied field, the magnetisation decreases as the grain size increases. A n approximate linear variation of resistivity and magnetoresistivity with g rain size allows the use of a simple 1D model to extract the intrinsic grai n magnetoresistance for these materials at T-c and to separate the grain an d grain boundary resistivity contributions. The relationship between resist ivity and magnetisation is discussed. (C) 1999 Elsevier Science B.V. All ri ghts reserved.