Effects on the physical properties of cation substitution in the layered cobaltites Y (Ba1 - x Cax) Co2 O5.5

Abstract

In this work we study the physical properties of the layered cobaltites YBaCo2 O5.5, focussing on the role of cationic disorder and size effects by a partial substitution of Ba by Ca. We have synthesized the polycrystalline compounds Y (Ba1 - x Cax) Co2 O5.5 with x = 0, 0.05 and 0.10. We characterized the samples within the 5-500 K temperature range, using neutron diffraction, magnetic measurements and electrical resistivity experiments. We have found the magnetic properties to be strongly affected by the cationic substitution. Although the "122" perovskite structure seems unaffected by Ca addition, the magnetic arrangements of Co ions are drastically modified: the antiferromagnetic (AFM) long-range order is destroyed, and a ferrimagnetic phase is stabilized below T ∼ 290 K. For the sample with x = 0.05 a small fraction of AFM phase seems to coexist with a ferrimagnetic one below T ∼ 190 K, whereas for x = 0.10 the AFM order is completely lost.