Large low-field magnetoresistance of a two-layered La2-2xCa1+2xMn2O7 polycrystal

Magnetotransport properties of a two-layered La2-2xCa1+2xMn2O7 (x = 0.2) po lycrystal have been studied as function of temperatures and applied fields. It was found that the variation of the resistivity with temperature at hig h temperatures obeys the variable-range hopping law under various applied f ields. Two maxima of magnetoresistance (MR) were observed under applied fie lds of I and 0.15 T, while no MR peaks were found under applied field of 0. 1 T. At 10 K, the MR attain as large as -17%. -25% and -30% under applied f ields of 0.05, 0.1 and 0.15 T, respectively. The large low-field MR at low temperatures can be attributed to the effects of the nearly fully spin-pola rized carriers' tunneling through the insulating (La,Ca)(2)O-2 layers betwe en the adjacent MnO2 bilayers. (C) 2001 Elsevier Science B.V. All rights re served.