Magnetoelectric properties and Morin type spin transitions of Na-doped GaFeO₃

The effects of Na doping on the structure magnetic, electric, and magnetoelectric properties of GaFeO₃were studied. Rietveld refinement of the XRD data reveals the formation of a single-phase trigonal structure with no impurity on Na doping up to 50% and a significant increase in lattice strain with doping. FTIR and Raman analysis further supported the phase purity of the samples. The morphology of the samples was studied using FESEM, and the particle size increased with Na doping. Magnetic data shows room temperature ferrimagnetic properties. Temperature-dependent magnetization measurements revealed a noticeable change from GaFeO₃, exhibiting a Morin-like transition at 182 K for the lowest Na content. This AFM transition temperature increased to 217 K with the highest Na doping levels. The temperature-dependent Raman spectra do not reveal any structural phase transition and show a distinct change in phonon modes near the spin reorientation temperature. The leakage current density of the samples at 100 volts increased from 10^-8A cm^-2to (10^-4-10^-5A cm^-2) with Na doping. The frequency-dependent dielectric constant increased largely with doping. The magnetoelectric coupling coefficient measured at room temperature rises for<i>x</i>= 0.05 to (36.2 ps m^-1) and slowly decreases as Na concentration increases.