Composition dependent magnetism in novel triple perovskite Sr3MFeMoO9 (M=Mn, Co, Ni)

Triple perovskite Sr3MFeMoO9 (M=Mn, Co, Ni) ceramics have been prepared under flowing N2 steam. All compositions are single phase and have B-site cation ordering. However, the composition with M=Co shows denser microstructures with smaller grains, the average grain sizes are 700, 500 and 650 nm for M=Mn, Co, and Ni, respectively. The chemical states of the surface and interior Mn, Co, Ni, Fe, and Mo cations are analyzed carefully. Both the magnetization-magnetic field curves and magnetization–temperature curves confirm that all compositions show antiferromagnetic behaviors. The Néel temperature of M=Mn and Ni compositions are determined to be 24.4 and 49.5 K, respectively. However, M=Co composition shows two magnetic transition temperatures at 70.9 and 180.7 K, which is possibly attributed to that the Co cations have intermediate spin-state (3d6, S=1) and high spin states (3d6, S=2). Furthermore, the compositions show semiconductor-like behaviors and neglectable magnetoresistance in whole measuring temperature range. Our results may be helpful for designing novel magnetic materials and for understanding magnetic couplings in triple perovskites.