High-field magnetoresistance at interfaces in manganese perovskites

The low-field (LFMR) and high field (HFMR) magnetoresistance response of ceramic La2/3Sr1/3MnO3 (LSMO) samples having grain sizes diameters daimeter ranging from 10 mu m to 20 nm have been investigated. A limiting LFMR of about approximate to 30% is obtained for the diameter approximate to 0.5 mu m but no larger values are obtained by further reduction of the grain size down to the nanometric range. On the contrary, the HFMR progressively rises when reducing the grain size. Magnetic and transport measurements suggest that HFMR originates from the existence of a noncollinear surface layer, having a thickness t that increases when reducing diameter. We have disclosed a clear relationship between the thickness, the intergranular resistance, and the height of the surface energy barrier. In addition, we show that in samples with submicronic grains, there is an intergranular Coulomb gap.