Abstract
The La0.8-xTbxCa0.2CoO3 cobaltites of orthoperovskite Pbnm structure were investigated by the X-ray and neutron diffraction, specific heat, and magnetization measurements. The terbium doping has two important effects, it increases the size disorder on perovskite A-sites and influences the magnetic properties due to large Ising-type moments (8.9 Bohr magnetons per Tb).
The compounds show a bulk magnetic moment below TC=82 K, 53 K, and 30K for x=0.1, 0.2, and 0.3, respectively. The neutron diffraction evidences a long-range ferromagnetic arrangement of cobalt moments, combined below 20 K with ordering of terbium moments in a canted arrangement.
A homogeneous magnetic phase is proved for the x=0.1 sample, while x=0.2 and 0.3 are in an intrinsically non-homogeneous magnetic state with long-range ordering only comprising 55% and 30% of the sample volumes. The ac susceptibility experiments prove a glassy character of the terbium doped samples and provide arguments for the short-range ordering above TC and wide distribution of relaxation times.