Lanthanum-doped Bi5Fe0.5Co0.5Ti3O15 multiferroic Aurivillius phase with improved magnetization

Bi4.2La0.8Fe0.5Co0.5Ti3O15 multiferroic ceramic system was obtained by conventional solid-state reaction method. Structural characterization from X-ray diffraction has revealed a reduction of the unit-cell volume after the incorporation of lanthanum into the structure. Raman spectroscopy exhibits local structural distortions for BO6 octahedrons in correspondence with the orthorhombic symmetry, related to the lanthanum incorporation and the partial substitution of Fe3+ by Co3+. An improved magnetization (1.1 emu/g at 15 kOe) has been obtained from the magnetic hysteresis measurements at room temperature, and in spite of the presence of magnetic secondary phases, the observed improvement can be attributed to the main Aurivillius phase. It can be explained from the influence of the La3+ doping over the Fe3+-O-Co3+ magnetic coupling. The change in slope for the real dielectric permittivity around 102 °C is associated to a magnetic transition of the Aurivillius phase. The reduction of this temperature could be related with the increase of the lanthanum content. The ferroelectric and ferromagnetic phase transitions temperatures were obtained from the differential scanning calorimetry and the thermomagnetic study.