Structural, magnetic and sensing properties of lanthanum ferrite via facile sol gel oxalate precursor route

Nanocrystalline lanthanum orthoferrite (LaFeO₃) powders have been synthesized using the oxalic acid precursor route. The ferrite precursors were obtained by the auto combustion of aqueous mixtures of lanthanum nitrate and ferric chloride in the presence of oxalic acid as a fuel. This precursor was annealed at different temperatures ranging from 400 to 1200 °C for 2 h. The effect of annealing temperature on the formation, crystalline size, morphology and magnetic properties were systematically studied. The powders formed were investigated using X-ray diffraction, Field emission scanning electron microscope and vibrating sample magnetometer. The results showed that the single-phase LaFeO₃ powders were obtained from 800 °C. The average crystalline size increased with increasing the annealing temperature up to 1000 °C. The average crystalline size varied from ≈54.7 to ≈168 nm with the annealing temperature. The saturation magnetization of the ferrite powders was continuously decreased with the increase in annealing temperature up to 1200 °C. The sensing properties for LaFeO₃ nanoparticles were examined by modification of carbon paste electrode by LaFeO₃. The cyclic voltammograms gave a well-defined redox peaks for K₃[Fe(CN)₆]/K₄[Fe(CN)₆] with significant higher peak current values. This may be due to the presence of LaFeO₃ which increased the catalytic properties for the prepared sensors by increasing the surface area of the sensor in presence of LaFeO₃ nanoparticle oxides which facilitate the formation of Fe(II)/Fe(III) redox couple.