Investigations of the magnetic properties and structures of the pillared perovskites, La 5Re 3MO 16 ( M=Co, Ni)

Abstract

La 5Re 3CoO 16 and La 5Re 3NiO 16 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 La 5Re 3CoO 16 at 35 K, and at 38 and 14 K for La 5Re 3NiO 16. 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 La 5Re 3CoO 16, the Co 2+ and Re 5+ 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 La 5Re 3MnO 16 and La 5Re 3FeO 16. In the case of the Ni material, the Re 5+ and Ni 2+ 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 La 5Re 3 MO 16 series, with M=Mn, Fe, Co, Ni and Mg are also reviewed.