Abstract
Magnetization and electrical transport properties of La0.60Ba0.40MnO3—γ (0 ≤ γ ≤ 0.20) anion-deficient manganites have been studied. Magnetic ordering temperature decreases insignificantly with γ in contrast to spontaneous magnetization. Ferromagnetic metallic ground state of stoichiometric samples (γ = 0) is destroyed gradually with increasing oxygen vacancy concentration (to γ = 0.20). It is shown that the long-range ferromagnetic order remains for γ ≤ 0.10 while the cluster spin glass properties appear for 0.10 < γ ≤ 0.20 with temperature of cluster moment freezing of 40 K. Electrical resistivity behavior of the samples with 0 ≤ γ ≤ 0.10 correlates with magnetization. Below the magnetic ordering temperature the resistivity becomes of metallic type and a peak of magnitoresistance is observed. The strongly reduced samples (0.10 < γ ≤ 0.20) have the activated type resistivity and exhibit a large magnetoresistance below the temperature at which the spontaneous magnetization occurs. For the explanation of the obtained results it is assumed that both the Mn3+–O–Mn3+ and the Mn3+–O–Mn4+ magnetic interactions become negative near the oxygen vacancies. The magnetic state of the anion-deficient samples is interpreted basing on the superexchange interaction model.
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