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.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 indu...

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

The effect of aliovalent Pb2+ dopant on the magnetic and magneto dielectric properties of LaFeO3 solid solutions

La1-xNaxFeO3(x=0.00 and 0.05) were synthesized by sol-gel auto-combustion method. No evidence of impurity phase and the peak (121) slightly shift towards lower angle is confirmed by X-ray diffraction analysis (XRD). The UV-visible spectra show strong absorption peak centered at approximately 231 nm and the calculated optical band gap are found to be 2.73eV, 2.36eV for x = 0.00 and 0.05, respectively. The M-H loop of pure sample is anti-ferromagnetic, whereas those of the Na doped sample shows enhanced ferromagnetic behavior. The remnant magnetization (Mr), saturation magnetization (Ms) and coercive field (Hc) of Na-doped sample are enhanced to 1.06emu/g, 5.39emu/g and 182.84kOe, respectively.La1-xNaxFeO3(x=0.00 and 0.05) were synthesized by sol-gel auto-combustion method. No evidence of impurity phase and the peak (121) slightly shift towards lower angle is confirmed by X-ray diffraction analysis (XRD). The UV-visible spectra show strong absorption peak centered at approximately 231 nm and the calculated optical band gap are found to be 2.73eV, 2.36eV for x = 0.00 and 0.05, respectively. The M-H loop of pure sample is anti-ferromagnetic, whereas those of the Na doped sample shows enhanced ferromagnetic behavior. The remnant magnetization (Mr), saturation magnetization (Ms) and coercive field (Hc) of Na-doped sample are enhanced to 1.06emu/g, 5.39emu/g and 182.84kOe, respectively.

The enhancement in optical and magnetic properties of Na-doped LaFeO3

Among those Fe-based perovskite $$R \hbox {Ba}_{2} \hbox {Fe}_{3} \hbox {O}_{8+\delta }$$
 which are isomorphous to high-
 $$T_{c} \, R \hbox {Ba}_{2} \hbox {Cu}_{3} \hbox {O}_{7-\delta }$$
 superconductors (
 $$R=\hbox {rare earth}$$
 and Y), the cubic $$\hbox {LaBa}_{2} \hbox {Fe}_{3} \hbox {O}_{8+\delta }$$
 is special in that both its magnetism and resistivity are strongly modified when varying a control parameter such as oxygen concentration (
 $$8+\delta$$
 ), La/Ba ratio (
 $$1 + x/2 - x$$
 ), or applied pressure (p). With the aim of identifying and optimizing those conditions that induce a reduction in its magnetism and resistivity, we synthesized various samples of $$\hbox {La}_{1+x} \hbox {Ba}_{2-x} \hbox {Fe}_{3} \hbox {O}_{8+\delta }$$
 and studied their structure, magnetism, and resistivity as a function of $$\delta$$
 , p, and x. In this preliminary report, we show that (i) the cubic, $$Pm{\bar{3}}m$$
 , structure is stable across the studied ranges, however the lattice a-parameter is reduced on increasing x, $$\delta$$
 , or p; (ii) the resistivity is reduced on increasing $$\delta$$
 or reducing x; the influence of pressure, on the other hand, is mostly manifested around and below the onset points of charge and magnetic order. (iii) The magnetism is much reduced as compared to that of the heavier $$R \hbox {Ba}_{2} \hbox {Fe}_{3} \hbox {O}_{8+\delta }$$
 members. We discuss the influence of each of x, $$\delta$$
 and p in terms of the Fe ions disproportionation scenario.

Influence of chemical substitution and pressure on structure, resistivity and magnetism of La1+xBa2−xFe3O8+δ (x = 0, 0.5, 1; 0 < δ < 1)

We report multifunctional properties of the charge disproportionate correlated electronic system La0.5Ba0.5FeO3 synthesized by conventional solid state reaction route. The bulk sample undergoes semiconductor–metal like transition at TSM = 102 K showing appreciable magnetoresistance (∼20%) around TSM even at a low field (∼0.5 T). A crossover of electrical conduction mechanism from Mott’s variable range hopping to small polaron hopping occurs around 210 K, well above TSM. Analysis of the transport, magnetic susceptibility, and magnetization data in the light of de Gennes proposal indicates the formation of canted antiferromagnetic spin order preceded by charge ordering in La0.5Ba0.5FeO3. Nonsaturation behavior and nonlinearity of the M-H curve at low temperature and at high field (∼5 T), confirms the canted spin order. The observed resistive transition is considered to be associated with the onset of weak ferromagnetic ordering in the canted antiferromagnetic spin state of the materials. Moreover, novel fer...

Resistive transition, anomalous magnetocapacitance, and ferroelectric phenomena observed in charge ordered canted antiferromagnetic La0.5Ba0.5FeO3 perovskite

K. Hsiao

Papers

Resistive transition, anomalous magnetocapacitance, and ferroelectric phenomena observed in charge ordered canted antiferromagnetic La0.5Ba0.5FeO3 perovskite