Phase Coexistence And Magnetic Behavior In The Low-Dimensional Hexagonal Cobaltites Ba(X)A(1-X)Coo(3-Delta) (A = Mg Or Ca And 0 <= X <= 0.20)

In this work, we report on X-ray diffraction and magnetization measurements carried out in the low-dimensional hexagonal cobaltites Ba(x)A(1-x)CoO(3-delta) (A = Mg or Ca, 0 <= x <= 0.20 and delta = 0 or 0.4). Polycrystalline samples have been synthesized by solid-state reaction. The Rietveld refinements of the X-ray diffraction patterns show clearly a phase coexistence of both BaCoO2.6 and BaCoO3 hexagonal polytype structures (space group: P63/ mmc), which is dependent on both the dopant ion and doping level. At low temperatures (T < 50 K), the ZFC-FC data recorded at H = 1 kOe for Ca-doped (x < 0.15) and Ba0.80Mg0.20CoO3-delta samples present a broad peak and strong thermal hysteresis. Besides, a second anomaly around room temperature is also observed in susceptibility curves for all samples. Further increasing in the Ca-doping produces a continuous decreasing of magnetization and for the samples with x > 0.10 the low temperature hysteresis is not observed anymore. The field-dependence of ZFC-FC curves taken for the sample grown with x = 0 show a displacement of the peak position into low temperature region. Except for the sample grown with x = 0.20, the MvsH loops taken at T = 2 K show multiple steps in the field region ranging -15 <= H <= 15 kOe. Finally, the saturation magnetization values are consistent with a low-spin state for the Co2+ or Co4+ ions. (C) 2017 Elsevier B.V. All rights reserved.