Magnetic phase transitions in the anion-deficient La_{1 <i>x</i>}Ba_<i>x</i>MnO_{3 <i>x</i>/2}(0 <i>x</i> 0.50) manganites

Abstract

The crystal structure, magnetization and electrical resistivity properties of the anion-deficient La1−xBaxMnO3−x/2 (0 ≤ x ≤ 0.50) perovskite manganites without Mn4+ ions have been investigated. It is established the reduced samples in the region 0 ≤ x ≤ 0.05 are O'-orthorhombic perovskites, in 0.10 ≤ x ≤ 0.25 they are rhombohedric whereas in 0.27 ≤ x ≤ 0.50 they are cubic. It is found that, as the x doping level increases, the samples undergo a transition from a weak ferromagnetic state (x = 0) to an inhomogeneous ferromagnetic one, (x ≥ 0.03) being a mixture of antiferromagnetic and ferromagnetic phases. At x ≥ 0.12 competition between antiferromagnetic and ferromagnetic interactions leads to a cluster spin glass state appearance with a magnetic moment freezing temperature of ∼ 45 K. The dominant magnetic phase for x ≥ 0.22 is supposed to be antiferromagnetic. All the reduced samples are semiconductors and show considerable magnetoresistance over a wide temperature range in a magnetically ordered state. The largest magnetoresistance (∼ 34% in a 9 kOe field at liquid nitrogen temperatures) is observed for an x = 0.30 sample. The magnetic phase diagram of La1−x3+Bax2+Mn3+O 3−x/22− manganites has been established by combining the results of magnetic and electrical measurements. The results obtained could be understood in terms of the phase separation and the 180° superexchange Mn3+–O–Mn3+ interaction model.