Magnetic behaviour governed by Co spin transitions in LaCo_1−<i>x</i>Ti_<i>x</i>O₃(0 ⩽<i>x</i>⩽ 0.5) perovskite oxides

Abstract

Perovskite-type cobaltites LaCo1−xTixO3 (0 ⩽ x ⩽ 0.5) synthesized by the liquid mix technique were characterized by x-ray diffraction, neutron diffraction, XPS, magnetic susceptibility and magnetization versus magnetic field measurements. Structural symmetry changes from rhombohedral (S.G. ) for 0.05 ⩽ x ⩽ 0.20 to orthorhombic (S.G. Pbnm) for 0.25 ⩽ x ⩽ 0.40. The bond distances dependence on the composition, x, has been analysed from x-ray and neutron diffraction data. Both the structural and the spectroscopic (from XPS) results suggest that Ti4+ substitution implies the stabilization of low-spin CoIII ions and the evolution of magnetic moments in the paramagnetic zone is also coherent with this assumption. For small values of x both FM responses and the absence of saturation in the M versus H curves at 2 K are interpreted in terms of a magnetic frustration. For x > 0.25 the cobalt cations seem to stabilize as CoIII (rather than Co3+) coexisting with Co2+. In these more substituted perovskites, AFM Co2+–O–Co2+ interactions become predominant, leading to a well established AFM ordering for x = 0.4 and 0.5.