Abstract
Composite bulk polycrystalline samples of Ag~δ~ –La~0.67~Sr~0.33–x –y~ Ag~x –δ~ Δ~y +δ~ MnO~3~ (x = 0.00, 0.15, 0.20, y = 0.00; and x = 0.15, y = 0.03, 0.05, with Δ representing cation vacancy at La site) were successfully synthesized using the sol–gel method. It is found that there are two phases in the samples, a cubic structure Ag phase and a perovskite phase. An experimental method for estimating the Ag phase content δ in the samples is presented. The Ag content x – δ and the cation vacancy y + δ were calculated. The Ag phase content and the lattice parameters of the two phases were also investigated using the Rietveld refinement method. The Ag phase contents obtained from the two methods are very close. The influences of x – δ and y + δ on the lattice parameters of the perovskite phase, the Curie temperature (T ~C~), the metallic–semiconducting transition temperature (T ~MI~), the magnetoresistance (MR), the peak temperature (T ~MR~) of the MR, and the temperature stability of the MR of the samples were examined. The Mn–O bond length L ~B~ of the perovskite phase increases with increasing x – δ . However T ~C~, T ~MI~, and T ~MR~ decrease with increasing L ~B~. For the sample Ag~0.07~–La~0.67~Sr~0.13~Ag~0.08~Δ~0.12~MnO~3~, under an applied magnetic field of 1.8 T, the MR is stable (9.41 ± 0.32%) in the temperature range 275–305 K; the MR increases linearly with magnetic field up to 1.5 T; and the change of MR with magnetic field, S ~MR~ = d(MR)/d(μ ~0~H ), is as high as about 5.2%/T. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)