Magnetic properties of the multiferroics Bi1−xCaxFe1−xMnxO3 and Bi1−xCaxFe1−xTixO3

This is a study of the crystalline structure and magnetic properties of the multiferroics Bi1−xCaxFe1−xMexO3 (Me = Mn, Ti). It is shown that Mn and Ti are in a quadrivalent state and the oxygen stoichiometry is conserved. The Me = Mn series undergoes a conversion at x = 0.19 from a polar rhombohedral phase (R3c) to a nonpolar orthorhombic phase (Pnma). A similar transition in the Me = Ti series was observed at x = 0.25. In both series, the polar phase (x ≥ 0.1) is weakly ferromagnetic. The spontaneous magnetization of the titanium series, however, exceeds that of the manganese series by more than a factor of three, despite the fact that Ti4+ is a diamagnetic ion. The residual magnetization of the titanium series decreases with rising temperature, while that of the manganese series increases anomalously within the interval 0.1 ≤ x ≤ 0.22. This behavior of the magnetic properties of the manganese series is explained by the extremely high sensitivity of the magnetic anisotropy to changes in the parameters of the crystal lattice, which leads to spin reversal.