High-field magnetoresistance at interfaces in manganese perovskites

The low-field (LFMR) and high field (HFMR) magnetoresistance response of ce ramic La2/3Sr1/3MnO3 (LSMO) samples having grain sizes diameters daimeter r anging from 10 mu m to 20 nm have been investigated. A limiting LFMR of abo ut 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 do wn to the nanometric range. On the contrary, the HFMR progressively rises w hen reducing the grain size. Magnetic and transport measurements suggest th at HFMR originates from the existence of a noncollinear surface layer, havi ng a thickness t that increases when reducing diameter. We have disclosed a clear relationship between the thickness, the intergranular resistance, an d the height of the surface energy barrier. In addition, we show that in sa mples with submicronic grains, there is an intergranular Coulomb gap.