Structural and multiferroic properties of Bi0.92−xHo0.08CaxFe0.97Mn0.03O3 thin film

Bi0.92−xHo0.08CaxFe0.97Mn0.03O3 (BHCxFMO) thin films were deposited on FTO/glass substrates using chemical solution deposition method. The crystal structure analyzed by X-ray diffraction, Rietveld refinement and Raman spectra reveals the structural transformation from rhombohedral R3c:H to triclinic P1 with co-doping. X-ray photoelectron spectroscopy analysis confirms that oxygen vacancy concentration in BHCxFMO thin films increases with the increase of Ca content due to the charge neutralization with Ca2+ doping at Bi3+ site. The frequency dependence of the dielectric response implies that dipoles of the charged defects rather than electrons/domains mainly contribute to the characteristics of εr and tanδ for BHCxFMO films. Among co-doped thin films, BHC1FMO thin film shows the highly enhanced ferroelectric properties with a giant remnant polarization value (Pr~88.18 μC/cm2), which is due to low leakage current in high electric field, improved breakdown characteristic and structure transformation. Moreover, BHC1FMO thin film presents enhanced magnetization (Ms=3.35 emu/cm3) in comparison to BFO thin film, which could be attribute to the suppression of spiral spin structure and/or the improvement in the canting angle of antiferromagnetically ordered adjacent planes arising from the disturbance of Fe–O–Fe bond angles due to the structural transformation. Raman results have further confirmed that (Ca, Ho, Mn) co-doping induces significant structural distortion of Fe–O bonds, which may cause internal structure distortion related to the change in bond length of the Fe–O and bond angle of Fe–O–Fe.