Effect of oxygen content on magnetization and magnetoresistance properties of CMR manganites

The influence of oxygen content on the magnetization and electrical resistivity of Ln₀.₅A₀.₅MnO₃ (Ln=La,Pr,Nd; A=Ca,Ba) manganites with the perovskite structure is investigated. It is shown that the La₀.₅Ca₀.₅MnO₃₋γ compound undergoes a sequence of transitions from an antiferromagnetic (γ=0) to a spin-glass (γ=0.17) state and then to an inhomogeneous ferromagnetic (γ=0.3) state. A transition from an antiferromagnetic charge-ordered state to a ferromagnetic charge-disordered state in Nd₀.₅Ca₀.₅ MnO₃₋γ is observed as the oxygen content is reduced to where γ=0.07. The Nd₀.₅Ba₀.₅ MnO₃₋γcompound shows an increase of the Curie point from 110 K (γ=0) up to 310 K (γ=0.3). In addition, a large magnetoresistance is revealed which develops below their Curie temperature despite the absence of Mn³⁺√Mn⁴⁺ pairs. A Zener double-exchange interaction is usually used in literature to explain the magnetic and electrical properties of hole-doped perovskite manganites. The data obtained support the mechanism of superexchange interactions between magnetic moments of the manganese ions via oxygen

Magnetic properties of the nonstoichiometric Sr-doped manganites

International audienceThe chemical phase content, crystal structure, and magnetization for the doped anion-deficient La1-xSrxMnO3-x/2 (x = 0, 0.05, 0.10, 0.20, 0.30) manganites have been studied. The samples undergo the structural phase transition from the O'-orthorhombic to the rhombohedric unit cell at x > 0.10. As doping level and oxygen deficiency increase the samples show a number of magnetic transitions. In the region of 0.05 ≤ x ≤ 0.20 the samples are inhomogeneous ferromagnets while at x = 0.30 they are cluster spin glasses. The temperature of the magnetic moment freezing is ∼45 K. The concentration dependences of the spontaneous magnetization and coercivity as well as magnetic phase diagram have been constructed. The magnetic properties of the anion-deficient Sr-doped samples may be interpreted on the basis of competition of the positive Mn3+(6)-O-Mn3+(6) and negative Mn3+(5)-O-Mn3+(6) isotropic superexchange interactions and impurity phase separation models. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Magnetic properties of the nonstoichiometric Sr-doped manganites

International audienceThe chemical phase content, crystal structure, and magnetization for the doped anion-deficient La1-xSrxMnO3-x/2 (x = 0, 0.05, 0.10, 0.20, 0.30) manganites have been studied. The samples undergo the structural phase transition from the O'-orthorhombic to the rhombohedric unit cell at x > 0.10. As doping level and oxygen deficiency increase the samples show a number of magnetic transitions. In the region of 0.05 ≤ x ≤ 0.20 the samples are inhomogeneous ferromagnets while at x = 0.30 they are cluster spin glasses. The temperature of the magnetic moment freezing is ∼45 K. The concentration dependences of the spontaneous magnetization and coercivity as well as magnetic phase diagram have been constructed. The magnetic properties of the anion-deficient Sr-doped samples may be interpreted on the basis of competition of the positive Mn3+(6)-O-Mn3+(6) and negative Mn3+(5)-O-Mn3+(6) isotropic superexchange interactions and impurity phase separation models. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim