Highly enhanced magnetic properties of BiFeO3 nanopowders by aliovalent element Ba-Zr co-doping

Highlights: • Phase-pure and well-crystallized Ba-Zr co-doped multiferroic BiFeO₃ nanopowders are harvested via sol-gel method. • The crystal structure transforms from R3c to R3c + P4mm. • The room-temperature magnetization hysteresis loops change to be soft ferromagnetic with co-doping. • The values of the maximum magnetization and remnant magnetization are up to 4.692 and 1.25 emu/g, respectively. Pure and Ba-Zr co-doped multiferroic BiFeO₃ nanopowders are synthesized via sol-gel method. X-ray diffraction demonstrates the transformation of crystal structure (from R3c to R3c + P4mm) and the absence of impurity phase. Scanning electron microscopy and transmission electron microscopy indicate that the co-doping leads to a decrease in particle size and the Bi_0.85Ba_0.15Fe_0.95Zr_0.05 sample has a particle size of 30–60 nm. Surprisingly, the room-temperature magnetization hysteresis loops change to be soft ferromagnetic with co-doping. The maximum and remnant magnetizations of the as-prepared nanopowders first increase and then decrease with increasing dopant concentration with the Bi_0.85Ba_0.15Fe_0.95Zr_0.05 sample having the best magnetic properties. The enhanced magnetization is due to the crystal lattice distortion caused by the ionic-radius difference between the substituent and host elements and the suppression of the antiferromagnetic spiral spin structure induced by the size effect of the nanopowders.