Abstract: Room temperature ferromagnetic Sr3YCo4O10.5+δ polycrystals with tetragonal structure were prepared by solid-state sintering method.The Sr3YCo4O10.5+δ polycrystals were characterized by thermogravimetricdifferential scanning calorimetry,X-ray diffraction and scanning electron microscopy.The results indicate that the final sintering temperature should be above 963 ℃,and the optimal sintering temperature was 1180 ℃ within our experiments.The Sr3YCo4O10.5+δ polycrystals show semiconductor behavior at 80-300 K,and the room-temperature resistivity reached its minimum of ～78.8 rΩ · cm with the optimal sintering temperature.The thermopower of polycrystals decreased with increasing temperature in at 317-1018 K,and the thermopower was 70.74 μV/K at 317 K.The magnetization-temperature curves and hysteresis loops showed that the spin states of internal Co3 +,magnetic domains and orientations of magnetic moments changed under the influence of applied magnetic field,temperature and crystal field,resulting in different magnetizations and magnetic states.With the applied magnetic field of 0.1 T,the Hopkinson peak with the largest magnetization of 0.46 emu/g was observed at 320 K in the ZFC curve,and the Curie temperature(Tc) was 323 K.While the largest magnetization of 1.1 emu/g was obtained at the Neel temperature(TN) of 264 K in the FC curve,and Tc was 320 K.The polycrystals all show room-temperature ferromagnetism in both ZFC and FC curves.

Key words: Room temperature ferromagnetic Sr3YCo4O10.5+δ polycrystals with tetragonal structure were prepared by solid-state sintering method.The Sr3YCo4O10.5+δ polycrystals were characterized by thermogravimetricdifferential scanning calorimetry,X-ray diffraction and scanning electron microscopy.The results indicate that the final sintering temperature should be above 963 ℃,and the optimal sintering temperature was 1180 ℃ within our experiments.The Sr3YCo4O10.5+δ polycrystals show semiconductor behavior at 80-300 K,and the room-temperature resistivity reached its minimum of ～78.8 rΩ · cm with the optimal sintering temperature.The thermopower of polycrystals decreased with increasing temperature in at 317-1018 K,and the thermopower was 70.74 μV/K at 317 K.The magnetization-temperature curves and hysteresis loops showed that the spin states of internal Co3 +,magnetic domains and orientations of magnetic moments changed under the influence of applied magnetic field,temperature and crystal field,resulting in different magnetizations and magnetic states.With the applied magnetic field of 0.1 T,the Hopkinson peak with the largest magnetization of 0.46 emu/g was observed at 320 K in the ZFC curve,and the Curie temperature(Tc) was 323 K.While the largest magnetization of 1.1 emu/g was obtained at the Neel temperature(TN) of 264 K in the FC curve,and Tc was 320 K.The polycrystals all show room-temperature ferromagnetism in both ZFC and FC curves.