MAGNETOCALORIC AND MAGNETIC PROPERTIES OF NANOCRYSTALLINE La₀.₇₅Pb₀.₂₅MnO₃ SYNTHESIZED BY HIGH ENERGY BALL MILLING

Abstract

Nanocrystalline La_0.75Pb_0.25MnO₃ powders were synthesized by grinding the constituent oxides in air at room temperature, using a high-energy planetary mill. The reaction process, evaluated by analyzing the evolution of the crystalline structure in the XRD patterns, is completed after about 12 h. The magnetic measurements indicate that the manganite nanoparticles with sizes smaller than 15 nm obtained by reacting milling have significant defects at the surface, leading to a serious decrease of the magnetic moments in comparison to the bulk material. A significant magnetocaloric effect was found at temperatures ranging from below to above room temperature, with the maximum entropy change located at temperatures near the magnetic transition one. The high RCP(S) values together with the broadened magnetic entropy curve suggest the possibility to use these materials for magnetic refrigeration devices.