Enhanced magnetic and magnetodielectric properties of Co-doped brownmillerite KBiFe2O5 at room temperature

We report significant enhancement in magnetic and magnetodielectric (MD) properties of cobalt (Co) doped polycrystalline KBiFe2O5 (KBFO). Rietveld refinement of X-ray diffraction data confirms monoclinic crystal structure with P2/c space group. SEM micrographs confirmed the polycrystalline nature of the samples with grain sizes varying from 1 µm to 5 µm. Raman spectra demonstrate the shifting of vibrational modes due to Co doping which is associated with FeO4 tetrahedral. The shift in vibrational modes due to Co doping is in line with the observed changes in FeO4 tetrahedral bond angles (O1-Fe-O1 & O1-Fe-O2) and bond lengths (Fe-O1 & Fe-O2) obtained from XRD data. Room temperature magnetization data reveal the maximum enhancement in Mr (~103 times) and Ms (~200 times) values for 5% Co-doped KBFO compared with KBFO. This enhancement in magnetization data is due to a spin-canted (Fe3+) antiferromagnetic spin structure and increased lattice strain with increased cobalt substitution. The temperature-dependent dielectric and magnetization data show an anomaly near 770 K (Tc) indicates the MD effect. Compared to KBFO, nearly ten times enhancement in MD and nearly 50 times reduction in magnetic loss (ML) is observed for KBFCO5 measured at 30 kHz frequency. Landau free energy approach confirms the biquadratic nature of MD coupling, and the strength is − 8 (emu/g)2 for 5% Co-doped KBFO and − 5(emu/g)2 for 10% Co-doped KBFO, respectively. The comparative study reveals that Co substitution in KBFO enhances maximum MD% and magnetization in 5% Co substitution. These results establish the coupling between electric and magnetic orders, which can find application in AC/DC magnetic field sensors and ME solar cells.