Microstructure evolution and magnetic properties of Eu doped CuFeO2 multiferroic ceramics studied by positron annihilation

A series of multiferroic ceramics CuFe1-xEuxO2 (x = 0-0.10) are prepared by traditional solid-state reaction. The effects of Eu doping on the microstructure, vacancy-type defects, and magnetic properties of CuFeO2 ceramics are investigated systematically by means of X-ray diffraction, Raman spectroscopy, scanning electron microscope, positron annihilation lifetime and physical property measurement system. The results show that no phase transition occurs in the entire range of doping content (x = 0-0.10), but the single phase structure is damaged by high Eu content (x = 0.04-0.10). Positron annihilation measurements indicate that the local electron density and the vacancy-type defect concentration increase gradually with the increase in Eu content from 0 to 0.08. Furthermore, abnormal changes in lifetime parameters can be found in x = 0.10 sample induced by the existence of impurity phase in the system. The magnetic measurements reveal that all the samples exhibit two successive magnetic transitions at T = 15 and 11 K. In x = 0.02 sample, the coexistence of ferromagnetism and antiferromagnetism can be found, and a maximum saturation magnetization of 11.548 emu/g at 5 kOe is achieved. The possible reasons for the above observations are discussed in detail.