Probing phase coexistence and stabilization of the spin-ordered ferrimagnetic state by ...

G. AURELIO; J. CURIALE; R. D. SÁNCHEZ; G. J. CUELLO

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

The American Physical Society

Año: 2007 vol. 76 p. 214417 - 214417

0163-1829

We study the effects of a partial substitution of Ba with the smaller cation Ca in the layered cobaltites YBaCo2O5+d for d~0.5. Neutron thermodiffractograms are reported for the compounds YBa0.95Ca0.05Co2O5.5 (xCa=0.05) and YBa0.90Ca0.10Co2O5.5 (xCa=0.10) in the temperature range 20 K¡ÜT¡Ü300 K, as well as high-resolution neutron diffraction experiments at selected temperatures for the samples xCa=0.05, xCa=0.10, and the parent compound xCa=0. 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 with spin state order is stabilized below T~290 K. For the sample with xCa=0.05 a fraction of AFM phase coexists with the ferrimagnetic one below T~190 K, whereas for xCa=0.10 the AFM order is completely lost. The systematic refinement of the whole series has allowed for a better understanding of the observed low-temperature diffraction patterns of the parent compound YBaCo2O5.5, which had not yet been clarified. A two-phase scenario is proposed for the xCa=0 compound which is compatible with the phase coexistence observed in the xCa=0.05 sample.