Probing phase coexistence and stabilization of the spin-ordered ferrimagnetic state by calcium addition in theY(Ba1−xCax)

Abstract

In this article we study the effects of a partial substitution of Ba with the smaller cation Ca in the layered cobaltites YBaCo2O 5+δ for δ ≈ 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 ≤ T ≤ 300 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.

Study and optimization of the synthesis routine of the single phase YBaCo2O6-δ double perovskite

“…This pattern was refined as a mixture of two phases having 3×2×2 and 1×2×2 superstructures. The former has tetragonal structure (s. g. P4/mmm) with cell parameters a = b = 11.596(4) Å and c = 7.509(7) Å whereas the latter has orthorhombic structure (s. g. Pmma) with cell parameters a = 3.821(4) Å, b = 7.846(2) Å, c = 7.515(8) Å in full agreement with available structural data [5,7,12,26,27].…”

Comparison of magnetic and thermoelectric properties of (Nd,Ca)BaCo2O5.5 and (Nd,Ca)CoO3

“…0.1 become fully FM. A similar decrease of that transition has been observed for YBa 1Àx Ca x Co 2 O 5.5 , 13 Ba is isovalent, therefore, the main mechanism for disappearance of the FM/AFM transition can be attributed to the local disorder. On the contrary to our samples, YBa 1Àx Ca xCo 2 O 5.5 does not demonstrate an increase in T C up to x ¼ 0.1.…”

Enhancement of the Curie temperature in NdBaCo2O5.5byA-site Ca substitution

“…Isovalent Ca substitution for Ba destroys the AFM long-range order and stabilizes the ferrimagnetic (FM) state. [16] Substitution of Ni for Co in GdBaCo 2-x Ni x O 5+δ strongly suppresses all the transition temperatures, [17] while…”