Magnetic state of Ba-doped manganites depending on the oxygen vacancy concentration

Abstract

Magnetization and electrical transport properties of La0.60Ba0.40MnO3-gamma (0 less than or equal to y less than or equal to 0.20) anion-deficient manganites have been studied. Magnetic ordering temperature decreases insignificantly with y in contrast to spontaneous magnetization. Ferromagrictic metallic ground state of stoichiometric samples (gamma = 0) is destroyed gradually with increasing oxygen vacancy concentration (to y = 0.20). It is shown that the long-range ferromagnetic order remains for gamma less than or equal to 0.10 while the cluster spin glass properties appear for 0.10 < gamma < 0.20 with temperature of cluster moment freezing of 40 K. Electrical resistivity behavior of the samples with 0 < gamma < 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 < gamma < 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.