Effect of iron doping on the magnetic structure ofTbBaCo2O5.5 layered perovskite

Abstract

The crystal and magnetic structures ofTbBaCo1.9Fe0.1O5.43 have been studied by neutron diffraction and magnetizationmeasurements. It is shown that spontaneous magnetization develops atTN = 305 Kand decreases abruptly below 200 K. The crystal structure is described in the space group Pmmm, ona 2ap*ap*2ap unit cell. It was shown that the extra oxygen vacancies are located mainly in the pyramidalsublattice, thus making tetrahedra. Magnetic structure in the high-temperaturemagnetic phase consists of ferromagnetic and G-type antiferromagnetic components,while in the low-temperature phase only the G-type component exists with a2ap*2ap*2ap magnetic unit cell. The ferromagnetic component results from canting magnetic moments ofCo3+ ions which were found to be predominantly in the high-spin statein pyramids. The refined values of the magnetic moments of theCo3+ ions in the octahedra indicate a mixed high–low-spin state. It is assumed thatnon-collinear magnetic structure results from a concurrence between positiveand negative exchange interactions as well as magnetocrystalline anisotropy inthe pyramidal sublattice. Using the concept of non-collinear magnetic structure,the giant anisotropic magnetoresistive effect in layered cobaltites is explained.