Structural, multiferroic properties and enhanced magnetoelectric coupling in Sm_1−xCa_xFeO₃

Sm_1−xCa_xFeO₃ where x=0, 0.25, 0.5, 0.75 and 1.0 was synthesized via the sol-gel method at low temperatures in steps of x=0.25. The as-prepared powders were characterized by Thermogravimetric Analysis (TGA), Transmission Electron Microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The as-prepared powders were pelletized and then sintered at 1000 °C/4 h to obtain single phase material. The sintered ferrite samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS). The XRD data reveal that a pure phase with perovskite structure is obtained for all the compositions and an exothermic peak appears in the DTA curve at 700 °C for x=0.25, suggesting a crystallization process; a similar behaviour is found to occur for the other compositions as well. The band gap values were determined from UV reflection spectra to be in the range of 1.8–2 eV. The structural transition is further confirmed by the changes observed in Raman vibrational modes. The microstructural characteristics of all the phases show particles of different morphology and size. The dielectric constant (ε_r) and dielectric loss (D) were decreased with an increase of frequency (40 Hz to 110 MHz). A huge enhancement in remnant magnetization (M_r) and coercivity (H_c) is observed as Ca³⁺ is increases. The improvement in the magnetic properties of present samples is due to the destruction of spin cycloid with Sm. No Fe⁴⁺ ions are discovered upon substitution of Sm³⁺ by Ca³⁺. Magnetic hysteresis loops of these samples show a significant weak ferromagnetic behaviour. Clear evidence of magneto-electric coupling is shown by the P–E loops measurement by applying an electric field.