Low temperature ferromagnetism in CaCu_3Ti_4O_(12)

The low-temperature magnetic order behaviors of perovskite oxide CaCu_3 Ti_4 O_(12)(CCTO) ceramics prepared by different methods are discussed.X-ray diffraction,scanning electron microscope,x-ray photoelectron spectroscopy,and direct current(DC) magnetization are used to characterize the structures,microscopic morphologies,valence states,and magnetic properties of the samples.The results show that the magnetic behaviors of CCTO ceramics are very sensitive to the preparation process.The quenched CCTO ceramic and CCTO powders grown in a molten salt crystal,which contain much more oxygen vacancies and Ti~(3+),show the coexistence of weak ferromagnetic order and antiferromagnetic order below the Neel temperature.It suggests that the bound magnetopolaron formed by oxygen vacancies and Ti~(3+) ion composite defects are responsible for the weak ferromagnetic order at low temperature.