High temperature magnetic behavior of multiferroics Bi1–xCaxFeO3

We investigate the room temperature microstructure and high temperature magnetic properties of Ca2+-substituted Bi1–xCaxFeO3 (0 ≤ x ≤ 0.2) ceramics. The Bi1–xCaxFeO3 compound transforms from rhombohedral into tetragonal structure with the phase boundary lying around x = 0.1. Based on this, the magnetic modulation becomes significant and the strongest remnant magnetization Mr is obtained at x = 0.1 compound. An important observation is the ferromagnetic-like phase transition revealed at TFM = 878 K in pure BiFeO3. The TFM of Bi1–xCaxFeO3 varies with Ca concentration and is close to the TAFM when x = 0.1. The convergence between TFM and TAFM implies the severe competition between Fe3+−O2−−Fe3+ and unbalanced Fe3+−O2−−Fe2+ antiferromagnetic exchange interactions, which leads to the dramatic change around TAFM in the M-T curve of x = 0.1 compound. The structure-related modulation of magnetic structure and complex interaction between Fe3+ and Fe2+ may be the driving force for the excellent magnetic properties ...