Magnetic and dielectric characterization of xBiFeO₃:(1-x)SrFe₁₂O₁₉ multiferroic composites

Multiferroic composites xBiFeO₃:(1-x) SrFe₁₂O₁₉ (0.5 ≤ x ≤ 1, Δx = 0.1) were produced by mixing powders of BiFeO₃ and SrFe₁₂O₁₉ obtained by high energy ball milling assisted with heat treatment. To study their multiferroic properties, the ferromagnetic, dielectric and magnetodielectric behavior was evaluated for each composite. The composites were produced using powders of BiFeO₃ and SrFe₁₂O₁₉ that were mixed, pressed at 800 MPa, and sintered at 700 °C for 4 h. XRD analysis confirms the presence of both ferroic phases, BiFeO₃ and SrFe₁₂O₁₉, and small amounts of the secondary phase, Bi₂Fe₄O₉ (mullite). The quantity of this secondary phase increases with the concentration of strontium hexaferrite. The remanent magnetization values are 17.9 emu/g and 2.54 emu/g for x = 0.5 and x = 0.9, respectively. The coercive field does not change with the composition; it exhibits a nearly constant value of 5.5 kOe for all the samples containing strontium hexaferrite. The addition of strontium hexaferrite produces diminution of the relative permittivity (ξ_r) and dielectric losses (tan δ). At 5 MHz, the composite with x = 0.9 shows the highest relative permittivity (16.78), and a diminution of dielectric loses of 43.88% due to the higher resistivity of the strontium hexaferrite. The magnetodielectric measurements showed an increase in the relative permittivity of the composites due to a reduction of the resistivity in agreement with the Maxwell-Wagner behavior when a magnetic field was applied. This study show evidence for magnetoresistive behavior by pure bismuth ferrite at room temperature, which has not been previously reported.