Investigations of the magnetic properties and structures of the pillared perovskites, La5Re3MO16 (M=Co, Ni)

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)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.

Powder neutron diffraction pattern of La5Re3NiO16 showing the new (0,0,1/2)(0,0,1/2) magnetic reflection. The inset shows the unusual magnetic structure, which has ferromagnetic intralayer coupling between Re (black spheres, black arrows) and Ni (grey spheres, grey arrows), whose moments are angled 45° in the ab plane and canted 30° from the c-axis, and antiferromagnetic interplanar coupling.Figure optionsDownload as PowerPoint slide