Magnetic and Transport Properties of Oxygen-Deficient Perovskite Manganites

Effects of oxygen deficiency on the magnetic and transport properties of La_2/3Ba_1/3MnO_3-δ polycrystalline perovskites have been investigated. As the nonstoichiometry parameter δ increases from 0.00 to 0.10, the lattice parameters at room temperature increase from 3.892(3)Å to 3.909(3)Å, the resistivity increases and the ferromagnetic ordering transition temperature shifts from 337 K to 268 K. A large magnetoresistance effect with -Δρ/ρ₀ of about 30% (955 kA/m, δ = 0.10) and a large magnetic entropy change of about 2.7 J/kg.K (796kA/m, δ = 0.00) is obtained in polycrystalline La_2/3Ba_1/3MnO_3-δ. The enhanced magnetoresistance effect at low temperature would be related to the grain boundaries of the polycrystalline samples.