Investigation of effect of Ni–Mg co-substitution on structural, optical, and magnetic properties of BiFeO3 nanoparticles grown by a sol–gel method (original) (raw)
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Multiferroic, magnetoelectric and optical properties of Mn doped BiFeO 3 nanoparticles
2012
Mn doped BiFeO 3 (5, 10 and 15 mol%) nanoparticles were synthesized using sol-gel technique. The influence of Mn doping on structural, dielectric, magnetic, magnetoelectric and optical properties of BiFeO 3 was studied. Rietveld refinement of XRD patterns showed rhombohedral to orthorhombic phase transition for 15 mol% Mn doped BiFeO 3 sample. Magnetic measurements revealed the enhancement of ferromagnetic property with increasing Mn doping in BiFeO 3 . The characteristic dielectric anomaly, expected in the vicinity of antiferromagnetic transition temperature T N (Neel temperature) was found in all Mn doped BiFeO 3 samples. The magnetoelectric coupling was evidenced by the change in capacitance with the change in the applied magnetic field. On increasing Mn concentration from 5 to 15 mol% in BiFeO 3 , a change in magnetocapacitance from 1.46% to 2.6% showed the improvement of multiferroic properties. In order to explore the optical properties of Mn doped BiFeO 3 nanoparticles, their photoluminescent properties were also investigated.
Solid State Sciences 102 (2020) 106168, 2020
BiFe 1-x Co x O 3 (x ¼ 0.00, 0.01, 0.03, 0.05 and 0.07) nanoparticles (NPs), were prepared by ethylene-glycol-based sol-gel technique. Phase purity of the NPs was confirmed by x-ray diffraction (XRD) technique. The average size of pristine BiFeO 3 (BFO) NPs was found to be 46 nm, which initially increased to 50 nm for 1% Co doping and then decreases to 48, 45 and 43 nm for 3%, 5% and 7% Co-doped BFO NPs, respectively. X-ray photoelectron spectroscopy (XPS) and M€ ossbauer spectroscopy confirmed that the oxidation state of Fe and Co is þ3. In the low frequency region, the dielectric constant (ε') shows a maximum decrease by 96% (137 → 5.1) on 5% Co-doping concomitant with 62% decrease in dielectric loss (0.32 → 0.12) which indicates substantial reduction in leakage current density. Further, the pristine BFO shows a well-defined dielectric loss peak at 40 Hz (tan δ ¼ 0.4). In contrast, twin dielectric loss peaks are uniquely observed for all the Co doped BFO NPs. 1% doped NPs show first and second peaks at 7 Hz and 20,400 Hz, respectively, which shifts to higher frequencies of 245 Hz and 154,000 Hz, on 5% doping. The magnetic measurements (M À H) revealed the ferromagnetic behaviour of the NPs. On Co doping, saturation magnetization (M s) increased with decrease in coercive field (H c). A maximum enhancement of 226% (0.93 → 3.05 emu/g) in M s values concomitant with decline of 61% in H c values (80 → 15 Oe) was observed for 7% doping. The reduction in leakage current and enhancement of magnetic properties makes the NPs better-suited for device applications.
Journal of Superconductivity and Novel Magnetism, 2014
Non-magnetic Zr 4+ ions substituted BiFeO 3 nanoparticles (BiFe 1−x Zr x O 3 , x = 0.0, 0.03 and 0.10) were synthesized by sol-gel method. X-ray diffraction and Raman studies indicate the rhombohedral phase for all the samples. The particle size decreases with increasing Zr 4+ concentration and varies in the range 20-50 nm. The absorption spectra show the strong absorption of visible light with optical band gap variation 2.27-2.21 eV for pure and Zr-doped BFO nanoparticles. A large saturation magnetization value of 9.33 emu/g is observed for x = 0.03 sample. The reduction in saturation magnetization for x = 0.10 sample is attributed to the dominant role of an increasing number of non-magnetically active Zr 4+ ions, and the formation of Fe-O-Zr coordination with increasing Zr 4+ ions concentration becomes less magnetic sublattice.
IEEE, 2016
Pure BiFeO3 nanoparticles were synthesized by a simple sol-gel method namely modified Pechini method. The nanoparticles were calcinated at four different temperatures (450 0 C, 550 0 C, 650 0 C, 750 0 C). Requirement for extra washing step for impurity phase reduction has been eliminated by elongation of the drying duration at oven from 12 hours to 28 hours along with intermediate grinding. FESEM and X-ray Diffraction (XRD) were performed which confirm that the samples calcinated at 450 0 C and 550 0 C show smaller particle size and greater correspondence. Hence XPS was performed on these two samples which showed lower oxygen vacancies for 550 0 C. Finally the SQUID analysis has been carried out for the 550 0 C sample. A higher value of remanent magnetization and coercive field at room temperature has been observed. Besides, an asymmetric shift in the field axis with unsaturated M-H curve may be attributed to the existence of exchange bias effect in the synthesized nanoparticles. Index Terms-Multiferroics, sol-gel, nanoparticles, exchange bias effect. I. INTRODUCTION The quest for multiferroic materials is actuated not only by the simultaneous existence of ferroelectricity and ferromagnetism but also by the possible coupling of their electric and magnetic orderings [1-3]. Such property allows mutual control of the electric polarization with a magnetic field or control of magnetization by an electric field. This magnetoelectric (ME) effect is prodigiously potential in developing novel memory and spintronic devices, spin valves, oscillators, filters, thin film capacitors and sensors [4-6]. Among the available multiferroic materials of type ABO3, BiFeO 3 (BFO) having rhombohedrally distorted perovskite structure with lattice parameters of a = 5.571Å and c = 13.868Å at room temperature with high Curie temperature of T C = 820-850 0 C [1, 2], Neel temperature of T N = 350-380 0 C [3] has turned into a cynosure of many current studies. It has potential applications of magnetoelectric coupling at temperatures around room temperature [1, 5, 7, 8]. In BFO Bi 3+ contributes to ferroelectricity whereas antiferromagnetism is attributed to Fe 3+ ions. BiFeO 3 exhibits anti-ferromagnetic G-type spin conf guration along the [111] c or [001] h directions in its pseudocubic or rhombohedral structure. It has a cycloid spin structure with a periodicity of
Materials Focus, 2014
In this work, the structural, optical, dielectric and magnetic properties of Bi 1−x La x FeO 3 nanoparticles (x = 0.50 and 0.75) have been investigated at room temperature. Structural analysis indicated the coexistence of orthorhombic (Pbnm) and rhombohedral (R3c) phases. UV-visible absorption spectra of the samples exhibit two doubly degenerate d-d transitions and three charge transfer transitions. Using diffused reflectance UV-Vis spectra, the direct and indirect band gaps of the samples decreases with increasing La content. The dielectric constant (ε) of the samples in the microwave region exhibited an anomalous phenomenon at room temperature. Magnetic hysteresis loops (M−H) of the samples exhibit weak ferromagnetism and an antiferromagnetic order. Additionally, the exchange bias effect was observed in these samples at room temperature. These results demonstrate that the method presented may be considered an effective way to improve the magnetic and optical properties of Bi 1−x La x FeO 3 .
Multifunctionality of magnetoelectrically coupled Ni/Cr co-doped BiFeO3 multiferroics
Journal of Alloys and Compounds, 2019
Co-doping in BiFeO 3 is supposed to be an effective approach to mediate its multiferroic characteristics, which are indispensable for its practical applications. In this regard, four compositions with general formula BiFe 0.9 Ni x Cr 0.1-x O 3 , with (x ¼ 0.02, 0.04, 0.06 & 0.08), were synthesized using sol-gel route followed by auto-combustion. X-ray diffraction analysis of the calcined samples exhibited rhombohedraly distorted perovskite structure with increase in lattice constant. Complex impedance spectroscopy distinguished the contribution of different electro-active regions in conduction phenomena. Hysteresis loops exhibited that tuning of Ni/Cr ratio had pronounced effects on the magnetic characteristics like saturation magnetization, remanence and coercivity. An appreciable variation in magnetoelectric coupling was also observed in the synthesized compositions. Hence, this research work presents a potential to improve the magnetoelectric coupling at room temperature which have many applications in spintronics for tunable multifunctional devices.
Journal of Alloys and Compounds, 2016
In this investigation, Gd and Mn co-doped Bi 0.85 Gd 0.15 Fe 1-x Mn x O 3 (x=0.0-0.15) nanoparticles have been prepared to report the influence of co-substitution on their structural, optical, magnetic and electrical properties. Due to simultaneous substitution of Gd and Mn in BiFeO 3 , the crystal structure has been modified from rhombohedral (R3c) to orthorhombic (Pn2 1 a) and the Fe-O-Fe bond angle and Fe-O bond length have been changed. For Mn doping up to 10% in Bi 0.85 Gd 0.15 Fe 1-x Mn x O 3 nanoparticles, the saturation magnetization (M s) has been enhanced significantly, however, for a further increase of doping up to 15 %, the M s has started to reduce again. The co-substitution of Gd and Mn in BiFeO 3 nanoparticles also demonstrates a strong reduction in the optical band gap energy and electrical resistivity compared to that of undoped BiFeO 3 .
2015
Structural, optical and magnetic properties of BiFeO 3 and Bi 0.9 Nd 0.1 Fe 0.95 TM 0.05 O3 (TM = Ni, Co) polycrystallines prepared by sol-gel method have been investigated. X-ray diffraction (XRD) patterns reveal that all samples crystalize in rhombohedrally distorted perovskite structure belonging to R 3C space group. The analysis results of both XRD and Raman scattering show the increase of lattice distortion with the co-replacing of Nd and TM ions into A and B sites respectively. All samples exhibit a weak ferromagnetic behavior at room temperature with the enhancement of the magnetization in Nd and TM co-doped samples.
We proposed Sol-gel method to study the structure, optical, magnetic and dielectric properties of Bi 1-x Ca x FeO 3 (x= 0.00, 0.01, 0.02, 0.03, 0.04 and 0.05) nano particles. The XRD spectrum exhibited predominant (012) and (110) orientation peaks at 2θ = 31.9 o and 2θ = 32.1 o corresponding to rhombohedral structure with R3c space group. From optical studies the band gap of BFO and Ca doped BFO nanoparticles were decreased from 2.13 to 1.96eV. The observed narrow band gap in the BFO system opens new vistas for the application of this material as multiferroic semiconductor. From magnetic properties the saturation magnetization for BFO (2.90 emu/gm) and for Ca doped BFO increased significantly from 1.00 emu/gm to 3.29 emu/gm. Dielectric and electric properties were studied over a frequency range of 10 Hz – 1 MHz. The dielectric constant was observed to decrease with increase in frequency. From cole-cole plots, as the Ca concentration increases, all semicircles become bigger and shift towards higher-frequency region, indicating a increment of grain and grain boundary resistance.