Effect of Al3+ substitution on the structural, magnetic, and electric properties in multiferroic Bi2Fe4O9 ceramics

Structural, magnetic, and electric properties have been investigated in polycrystalline Bi₂(Fe_1-xAl_x)₄O₉ (0≤x≤0.25) ceramics synthesized by a modified Pechini method. Structural analysis reveals that Al³⁺ doped Bi₂Fe₄O₉ crystallizes in orthorhombic structure with Pbnm space group. Surface morphology of the end products is examined by scanning electron microscopy and the grain size has a tendency to decrease with increase in Al³⁺ doping level. Compared with pure Bi₂Fe₄O₉, room temperature coexistent multiferroic-like behavior is observed in Al³⁺ doped Bi₂Fe₄O₉. By analyzing magnetic properties, the Néel temperature monotonously shifts to low temperatures from ~260 K (x=0) to ~35 K (x=0.25). Moreover, the spin dynamic measured by the shift in ac magnetic susceptibility as a function of frequency provides a possibility of spin-glass-like behavior, which is further confirmed by fitting the critical slowing down power law and memory effect.