Large magnetoresistance effect in isotropic polycrystalline perovskite-like La-AM-Mn-O (AM = K, Rb) ceramics

Polycrystalline isotropic perovskite-like La-AM-Mn-O compounds (AM = K, Rb) with trivalent La³⁺ partially substituted for pseudo-divalent cations (a half of trivalent La³⁺ plus a half of monovalent K⁺ or Rb⁺) were fabricated by conventional ceramic techniques, and their magnetoresistance effects and magnetic/electric properties were studied. All studied samples show ferromagnetism and high electrical conductivity at low temperature of 77 K. As sintering temperature increases, Curie temperature, saturation magnetization and resistivity decrease. Polycrystalline isotropic La-K-Mn-O sample shows a large negative magnetoresistance effect of -25% at H = 1.5 T and T = 280 K. This value is comparable to the value previously reported in La_1-xMe_xMnO₃ (Me = divalent cation) single crystal.