Quantification of charge carriers participating antiferromagnetic to weak ferromagnetic phase transition in Na doped LaFeO3 nano multiferroics

Abstract

Multiferroic La1-xNaxFeO3 (x = 0.0, 0.05, 0.10, and 0.15) nanoparticles have been synthesized by the citrate sol-gel auto-combustion method. It is uniquely known for the homogeneous distribution of particle size due to the low temperature synthesis condition. The Rietveld refinement of the X-ray diffraction pattern has exhibited the single phase orthorhombic perovskite structure. It is confirmed from micro-Raman analysis that hole doping (Na) produces a structural crossover from the Pnma to Pbnm space group. The red shift observed in UV-visible spectroscopy indicates the shrinkage of bandgap. Photoluminescence analysis supports independently the bandgap shrinkage by the existence of violet-blue emission due to charge disproportion by oxygen related defects. A changeover from semiconductor to metallic nature accompanied by the hopping of charge carriers from Fe3+ to Fe2+/Fe4+ exchange interaction has revealed a considerable increase in conductivity and dielectric constant. Finally, the doping helps to induce transition from an antiferromagnetic to a weak ferromagnetic state due to free carrier concentration. It is found that the hole driven Fe3+ to Fe2+/Fe4+ exchange interactions with change in the Bohr magneton values from 5.9 μB to 4.9/4 μB are responsible for variation in the magnetization values.

Combined Bottom-Up and Top-Down Approach for Highly Ordered One-Dimensional Composite Nanostructures for Spin Insulatronics

“…On the other hand, LFO has an orthorhombic Pnma -type structure, and it is reported to exhibit Raman modes between 400 and 450 cm –1 because of the bending vibration of the Fe–O 6 , whereas the mode corresponding to the stretching vibration of the Fe–O 6 appears above 500 cm –1 . 69 , 70 Raman peaks corresponding to the A 1g vibration of the rare-earth ion (La) are reported to be observed below 300 cm –1 .…”

“…The Raman peaks in the range of 550–720 cm –1 correspond to the A 1g mode, which appears due to the vibration of the Fe–O 4 /Co–O 4 tetrahedra, whereas the peaks appearing below 500 cm –1 are due to the E g and T 2g vibrations of the Fe–O 6 /Co–O 6 octahedra. On the other hand, LFO has an orthorhombic Pnma -type structure, and it is reported to exhibit Raman modes between 400 and 450 cm –1 because of the bending vibration of the Fe–O 6 , whereas the mode corresponding to the stretching vibration of the Fe–O 6 appears above 500 cm –1 . , Raman peaks corresponding to the A 1g vibration of the rare-earth ion (La) are reported to be observed below 300 cm –1 .…”