| Abstract | La5Re3CoO16 and La5Re3NiO16 were synthesized by solid-state reaction and studied by SQUID magnetometry, heat capacity and powder neutron diffraction measurements. These two compounds belong to a series of isostructural Re-based pillared perovskites [Chi et al. J. Solid State Chem. 170 (2003) 165]. Magnetic susceptibility measurements indicate apparent short-range ferri or ferromagnetic correlations and possible long-range antiferromagnetic order for La5Re3CoO16 at 35°K, and at 38 and 14°K for La5Re3NiO16. Heat capacity measurements of the Co compound show a lambda anomaly, typical of long-range magnetic order, at 32°K. In contrast, the Ni compound displays a broader, more symmetric feature at 12°K in the heat capacity data, indicative of short-range magnetic order. Low-temperature powder neutron diffraction revealed contrasting magnetic structures. While both show an ordering wave vector, k=(0,0,1/2), in La5Re3CoO16, the Co2+ and Re5+ moments are ordered ferrimagnetically within the corner-shared octahedral layers, while the layers themselves are coupled antiferromagnetically along the c-axis, as also found in La5Re3MnO16 and La5Re3FeO16. In the case of the Ni material, the Re5+ and Ni2+ moments in the perovskite layers couple ferromagnetically and are canted 30? away from the c-axis, angled 45? in the ab-plane. The layers then couple antiferromagnetically at low temperature, a unique magnetic structure for this series. The properties of the La5Re3MO16 series, with M=Mn, Fe, Co, Ni and Mg are also reviewed. |
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