New synthesis of polycrystalline La0.7(SrxCa1-x)0.3MnO3 by mechanical alloying

Using mechanical alloying we have successfully prepared polycrystalline samples of ferromagnetic La-0.7(SrxCa1-x)(0.3)MnO3 which exhibit a giant magnetoresistance (MR) effect. The influence of preparation on resistivity and the MR behavior has been investigated. Upon increasing the annealing temperature from 973 K to 1473 K, the compactness, grain size and metal-insulator transition temperature T-rho increase for the samples with x = 0.2, whereas the Curie temperature T-c is found to be less affected. All the La-0.7(Sr0.2Ca0.8)(0.3)MnO3 samples exhibit a large magnetoresistance ratio Delta rho/rho(0) at 77 K and a second maximum around the Curie temperature. For the La0.7Sr0.3MnO3 samples, with increasing temperature from 77 K to room temperature, the resistivity increases and the MR ratio decreases monotonically. (C) 1998 Elsevier Science Ltd. All rights reserved.