Bounded magnetic polarons induced enhanced magnetism in Ca-doped BiFeO3

Abstract

The structural, optical and magnetic properties of Bi1-xCaxFeO3 (0 ≤ x ≤ 0.25) nanoparticles synthesized via sol-gel method are investigated. A phase transition from the rhombohedral R3c structure (x ≤ 0.10) to the ideal cubic perovskite structure (x = 0.25) is observed. The grain size of the samples is first reduced to x = 0.05 and keeps constant with 0.05 ≤ x ≤ 0.10 by XRD refinement. With the increase of Ca2+ dopants, the oxygen vacancies increase while the content ratio of Fe2+ maintains constant. Due to the increase of the oxygen vacancies, the optical band gap in the visible region of the specimens decreases. The remanent magnetization is enhanced approximately linearly at the R3c phase region and reaches the maximum value of 0.096 emu/g at x = 0.10. The enhancement of magnetization at low doping content x can be attributed to the formation of the magnetic polarons bounded to the impurities.