Preparation, magnetoresistance and magnetocaloric effect of two-layered perovskite La $\scriptstyle \mathsf {}$ 2.5- x K $\scriptstyle \mathsf {}$ 0.5+ x Mn $\scriptstyle \mathsf {}$ 2O $\scriptstyle \mathsf {}$ 7+δ

Abstract

Polycrystalline two-layered perovskite La2.5-xK0.5+xMn2O 7 + δ (0 < x < 0.5) samples have been prepared by a modified sol-gel method and their magnetoresistance and magnetocaloric effects have been studied. A large deviation between the metal-insulator (MI) transition temperature (T ρ ) and the magnetic transition temperature (TC) is observed. Large magnetoresistance (MR) effects with Δρ/ρ of ∼40% at 12 kOe are obtained in wide temperature ranges. The maximum of the magnetic entropy change peaks at its Curie temperature (TC), far above its MI transition temperature (T ρ ). The large magnetic entropy change (∼1.4 J/kg.K) is obtained in the sample La2.5-xK0.5+xMn2O 7 + δ (x = 0.35) upon 10 kOe applied magnetic field.