resumo
Neutron powder diffraction studies of crystal and magnetic structures, magnetization and magnetotransport measurements have been performed for La0.5-xPrxBa0.5CoO3-delta (x <= 0.375, delta < 0.25) cobaltites. It has been found that the compositions (0 <= x <= 0: 35) are cubic (Pm3m) whereas x 0.375 one is tetragonal (P4/mmm) due to an ordering of rare-earth and barium ions, while the oxygen vacancies are disordered. The oxygen content decrease leads to transformation of the magnetic structure from ferromagnetic to the G-type antiferromagnetic one through the mixed two-phase magnetic state. The compositions with antiferromagnetic component show structural phase separation, strong increase of the unit cell volume upon cooling, and anomalous magnetization behavior. It is suggested that these phenomena are associated with stabilization of Co3+ ions in high/low spin state at low temperature. The high/low spin state corresponds antiferromagnetic phase, whereas in the ferromagnetic one, the Co3+ and Co4+ ions adopt intermediate spin state. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4733953]
palavras-chave
MAGNETIC-STRUCTURES; SPIN STATES; PEROVSKITE
categoria
Physics
autores
Troyanchuk, IO; Karpinsky, DV; Bushinsky, MV; Sikolenko, V; Efimov, V; Cervellino, A; Raveau, B
nossos autores
Dzmitry Karpinski (Karpinsky)
Bolseiro de pós-DoutoramentoGrupos
agradecimentos
The authors would like to acknowledge the financial support of the BRFFI (Grant No. T11D-003) and the FCT (Grant No. SFRH/BPD/42506/2007). This research project has also been partly supported by the European Commission under the Seventh Framework Programme through the Key Action: Strengthening the European Research Area, Research Infrastructures [Contract No. 226507 (NMI3)].