K. Saravana Kumar

A series of Europium orthoferrites, Eu_2-xFe_xO₃ (x = 0 – 0.5) are successfully prepared by employing solid state reaction technique. The structural analysis through powder X-Ray diffraction technique reveals the multiphase formation of all the prepared compounds. Further, the unit cell visualization of all the prepared compounds confirms the change of crystal structure from cubic to orthorhombic phase. The crystal structure analysis confirms the typical framework of Eu – Fe – O chains with unprecedented ratio of Eu³⁺ and Fe³⁺ ions. The optical properties of prepared compounds are investigated using photoluminescence (PL) analysis. Upon excitation at 495 nm wavelength, the emission spectrum of prepared compounds exhibits a broad band in the range of 500-700nm with maximum intensity peak at 548 nm (Blue – 2.26eV). Hence, the substitution of Fe³⁺ ion yields with intrinsic blue photoluminescence (⁵D₀ → ⁷F₀) of Eu³⁺ and is easily shielded by the substitution of Fe³⁺ which may be due to the closer conduction band gap of Eu³⁺ (2.26 eV) with Fe³⁺ (2.67 eV). The schematic energy level diagram for Fe³⁺ in the Eu³⁺ host matrix has been proposed for the better understanding of photoluminescence processes. The variation of intensity of PL peak between 500 and 700 nm for the substitution of Fe in the range of x = 0 – 0.5 yields with interesting optical properties for exploring new phosphor materials for optoelectronic device fabrications.

Phase pure NdFeO₃ has been achieved using high energy ball milling of oxide precursors with subsequent sintering. It is established that structural arrangement of NdFeO₃ regulates the multifunctional feature of the material. Rietveld refinement of the room temperature X-ray diffraction pattern shows that the Fe-O-Fe bond angle significantly favors the super exchange interaction, which is predominantly antiferromagnetic in nature. Magnetization measurement illustrates antiferromagnetic behaviour with a weak ferromagnetic component caused by the canted nature of the Fe³⁺ spins at room temperature. Absorption bands in the visible ambit, apparent from the UV-Vis diffuse reflectance studies, is found due to the crystal ligand field of octahedral oxygen environment of Fe³⁺ ions. The direct band gap is estimated to be 2.39 eV from the diffuse reflectance spectrum. The lossy natured ferroelectric loop having a maximum polarization of 0.23 μC/cm² at room temperature is found to be driven by the non-collinear magnetic structure with reverse Dzyaloshinskii–Moriya effect. Magnetic field has influence on the dielectric constant as evident from the impedance spectroscopy, indicating the strong coupling between ferroelectric and the magnetic structure of NdFeO₃.