Structural,optical, and magnetic evaluation of Co-, Ni-, and Mn-modified multiferroic BiFeO3 ceramics

Co-, Ni-, and Mn-doped BiFeO₃ (BFO) ceramics were synthesized herein through a solid-state reaction. All doped BFO samples exhibit visible-light response, and the Co- and Ni-doped BFO samples present enhanced ferromagnetic order at room temperature. All doped samples show secondary phases in minor quantities. Optical spectra reveal two absorptions bands, indicating multiple electron transitions for BFO and its secondary phases. M ? H hysteresis loops suggest enhanced ferromagnetism in the Co- and Ni-doped BFO samples because of magnetic spinel CFP and NFO phases, respectively, whereas changes in oxygen vacancies and Fe–O–Fe bond angle play minor roles in the ferromagnetic behavior.     

Preparations and tailoring of structural,magnetic properties of rare earths (REs) doped nanoferrites for microwave high frequency applications

Rare earths (Res) doped Mn spinel nanoferrites with nominal composition MnR_0.2Fe_1·8O₄ (REs = Tb, Pr, Ce, Y and Gd) were synthesized using sol gel method. FTIR, XRD and FESEM were employed to evaluate the structure, phase, vibrational bands, morphology, grain size and microstructure respectively. VSM was employed to investigate the magnetic features of the Mn nanoferrite and REs doped Mn nanoferrites. XRD confirmed the single-phase cubic structure of Mn nanoferrite whereas tetragonal phase was observed for all REs doped Mn nanoferrites. Unit cell software was used to determine the structural features such as lattice parameter, cell volume, ‘da’, ‘db’, ‘dc’ and ‘dv’ respectively. FTIR results demonstrated the absorption peaks of Mn and REs doped Mn ferrite at 647-674 cm⁻¹. FESEM results depicted the irregular shapes of the particles with large agglomerations in the prepared samples. The grain size evaluated by LIM (line intercept method) found in the range of 94 to 213 nm respectively. Saturation magnetization was increased from 1.332 to 38.097 emu/g whereas remanence was increased from 1.096 to 25.379 emu/g respectively. In addition, other magnetic parameters such as initial permeability, magnetic anisotropy and magnetic moments were also increased. Moreover, Y–K angles showed significant response with REs doping in Mn ferrites. Furthermore, high frequency response and switching field distribution (SFD) of Mn ferrite and REs doped Mn ferrites were also determined. It is found that Y doped Mn ferrite depicted better high frequency and SFD response as compared to Mn ferrite and REs doped Mn ferrites. The coercivity of all these pure Mn ferrite and rare earth's substituted Mn ferrites (425–246 Oe) was higher as compared to the pure Mn and yttrium substituted Mn ferrite (107–217 Oe. Therefore, it was suggested that Y doped Mn ferrite was more suitable candidate for switching, and high frequency absorption applications in microwave regime.     

Effect of Gd3+ doping on structural,optical and magnetic properties of SnO crystals

Layered dilute magnetic semiconductors are expected as promising candidates for next-generation electric devices, however, the low saturation magnetization limits their applications. Doping of semiconductors can effectively tune the magnetic and optical properties, which further influence on spintronic and optoelectronic applications. The discovery of layered materials opens a new door for spintronic application due to their unique properties. Here, the layered Gd³⁺ doped SnO crystals are synthesized via a simple hydrothermal method, with morphologies ranging from square shapes to four-pointed star shapes. We investigated the UV–vis absorption spectra, photoluminescence spectra and magnetic characteristics of the samples. The as-obtained Gd³⁺ doped SnO crystals show robust ferromagnetism at room temperature. From the first-principles calculations results, the substitution Gd dopants and the O vacancies work together to introduce the ferromagnetism. Our results demonstrate the Gd³⁺ doping tunability of SnO, a ferromagnetic layered material, as a functional material for spintronics and optoelectronics.     

Optical and structural properties of X-doped (X = Mn,Mg, and Zn) PZT nanoparticles by Kramers–Kronig and size strain plot methods

Pure and X doped (X = Mg, Mn, and Zn) lead zirconate titanate nanoparticles (PZT-NPs) were synthesized using sol-combustion method. The xerogel was calcined at temperature of 700 °C for 2 h. The structure of the prepared powders is characterized using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The XRD results show that the PZT-NPs are formed in perovskite structure with rhombohedral phase. In addition, a small shift was detected in XRD patterns of doped PZT-NPs. Also, the XRD results were analyzed using size strain plot (SSP) to calculate the lattice strain of the prepared samples, which revealed that the lattice strain depends on the different ionic radii of the dopants. To have a better understanding of the optical properties of the pure and doped PZT-NPs, the obtained FTIR spectra were analyzed using Kramers–Kronig method. The results show that there are certain relations between the optical parameters and the wavelength of the incident beam as well as the optical modes. Also, the value of the pure and doped PZT-NPs optical band gaps were estimated using ultra violet and visible (UV–vis) spectroscopy. It was found that the optical properties of the doped samples depend strongly on dopants.     

Preparation of polyaniline/nickel oxide nanocomposites by liquid/liquid interfacial polymerization and evaluation of their electrical,electrochemical and magnetic properties

A novel route has been developed to synthesize polyaniline (PANI)/nickel oxide (NiO) nanocomposites via liquid/liquid interfacial polymerization where NiO and the initiator were dispersed in the aqueous phase and the monomer was dissolved in the organic phase. The synthesized samples were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, ultraviolet?visible absorption, X‐ray diffraction, and electrochemical, electrical conductivity and magnetic property measurements. NiO was dispersed uniformly within the PANI matrix. The composites exhibited noticeable improvement in thermal stability and electrical conductivity in comparison with pure PANI. The composites showed excellent electrochemical reversibility at a scan rate of 0.1 V s^?1 and good redox stability even up to 100 cycles. The room temperature magnetic hysteresis measurements show a low value of coercivity for the polymer composites in comparison with NiO. The remnant magnetization (M_r) values were found to be increased with increasing concentration of NiO in the composites. © 2013 Society of Chemical Industry     

Structural,Optical, and Magnetic Properties of Nd‐Doped GaN Powders

Nd‐doped GaN powders are synthesized by a direct nitridation of Ga₂O₃, and the structural, optical, and magnetic properties of the products with different Nd concentrations are investigated. It is found that the Nd‐doped GaN powders have wurtzite structure and exhibit a broad blue emission related with defects. The stable room‐temperature ferromagnetism is observed in the products, which is dependent on the Nd concentration. The possible origin of the ferromagnetism is discussed.     

Fe–Co co-doping effects on antiferromagnetic core of NiO nanoparticles

The Fe and Co single and co-doping effects on the structural and magnetic properties of NiO nanoparticles (NPs) have been studied. The Fe and Co doping into NiO system did not induce any other possible secondary phase (other than NiO) and the average crystallite size was found to be in a narrow range of 33–40 nm which is suitable for studying the doping effects. Room temperature ferromagnetic resonance (FMR) measurements demonstrated the existence of a net magnetization in antiferromagnetic (AFM) NiO NPs which was observed to be increased with an increasing Fe doping and decreasing Co doping concentration. The scattered differential FMR signal for 8% Co doped NiO NPs revealed the presence of randomly oriented magnetic moments in the core of the NPs. However, decreasing the Co doping concentration and increasing the Fe doping concentration increased the degree of homogeneity of the spin structure in the system. The M ? H loops taken at room temperature with S-like shape confirmed the presence of a weak ferromagnetism in the Fe doped samples in accordance with FMR analysis and attributed to the double exchange mechanism in these NPs. In ZFC/FC curves, a small peak at low temperatures, in the range of 9–18 K for all the samples, indicates the magnetization contribution from the uncompensated surface spins of these NPs. In addition, a relatively broad peak for higher Fe doping concentrations at higher temperatures indicates the onset of magnetization from the core of these NPs, where Fe and Ni ions may couple parallel or anti-parallel to each other. In summary, Co–Fe co-doping induced a core magnetization in AFM NiO NPs system and makes it attractive for various magnetic applications.     

Band gap modulation and improved magnetism of double perovskite Sr2KMoO6 (K = Fe,Co, Ni,Mn) doped BaTiO3 ceramics

BaTiO₃ ceramics doped with double perovskite Sr₂KMoO₆ (BT-SKM) are fabricated via solid-state reaction technology. The effects of SKM dopants on the structure, band gap and electrical/magnetic properties of BT are systematically studied. XRD and Raman spectra analysis show polycrystalline perovskite structure of the samples, which confirms the structural changes. With the addition of SKM dopants, the grain size of the samples decreases significantly. The band gaps of doped BT samples reduce, and the minimum band gap of BT-SCM is 1.77 eV, which is apparently reduced compared with the band gap of pure BT of 3.22 eV. However, the ferroelectric properties are weakened in samples doped with SKM. This ascribes to the introduction of more oxygen vacancies by dopants, which impedes the switching of domains, resulting in deterioration of ferroelectric properties. Furthermore, ferromagnetism of BT-SNM is observed, which may be attributed to the long-range exchange interaction between Ni²⁺ ions and oxygen vacancies. These results reveal the potential applications of these perovskite oxides in photovoltaic and memory devices.     

Structural, electronic and magnetic properties of Sn0.95Ni0.05O2 nanorods

With a view to investigate the structural, electronic and magnetic properties of Ni (5%) doped SnO(2) diluted magnetic semiconductor nanorods prepared by a PEG-6000 assisted wet chemical route, a systematic investigation has been carried out. The micro structural properties were investigated by Rietveld refinement of XRD data, AFM, TEM, EDS, SAED, FTIR, Raman scattering and XPS measurements. These studies revealed that Sn0.95Ni0.05O2 nanorods have a polycrystalline single phase tetragonal rutile structure without any detectable impurity phases and the aspect ratios of the nanorods are in the range 2.85-10.2. The deconvoluted XPS core level Ni 2p spectral studies determined the oxidation state of Ni as +2. The nanosize effects and local defects are found to influence the local electronic structure of materials. From M-H, M-T, magnetic force microscopy (MFM) and ESR studies, all the samples are found to exhibit clear room temperature ferromagnetism without any metallic clusters. The magnetization behaviour is found to depend on the overlap of percolated bound magnetic polarons and their interactions with dopant induced defects. The magnetic exchange interactions are found to depend on the aggregation behaviour of nanorods, exchange media, the surface diffusion behaviour of randomly distributed Ni ions and the modification of electronic structure.     

高频热等离子体制备Mn掺杂的棒状纳米氧化锌

以锌粉和MnCl2为反应物,在高频感应热等离子体中制备了Mn掺杂的ZnO纳米棒. 通过XRD, FESEM, TEM和HRTEM对产物的结构、形貌进行了分析. 随着Mn掺杂量的增加,ZnO的衍射峰向小角方向移动,证实掺杂的Mn原子进入了ZnO晶体的晶格,ZnO纳米棒的长径比逐渐减小,未掺杂的ZnO纳米棒直径约为30 nm,长度约为2 mm,当掺杂的Mn/Zn摩尔比为4%时,掺杂后的ZnO纳米棒直径约为100 nm,长度约为200 nm. Mn掺杂的ZnO纳米棒显示出了室温铁磁性特征,且随Mn掺杂含量提高而增强,当Mn掺杂量由0.25%增加到4%时,ZnO纳米棒的矫顽力从78 Oe上升到149 Oe.     

施、受主掺杂对高居里点BaTiO3基PTCR陶瓷材料性能的影响

以合成的(Ba_(0.6)Pb_(0.4))TO_3为主要原料,通过电性能测试、SEM、XRD等手段分析研究了施主Nb~(5 )掺杂以及施主Nb~(5 )、受主Mn~(2 )共掺对高居里点BaTiO_3基PTCR陶瓷材料性能的影响。结果表明,施受主掺杂不影响材料基体的晶体结构,适量的施主Nb~(5 )掺杂可降低材料的室温电阻率从而改善其性能,受主Mn~(2 )掺杂提高了施主Nb~(5 )掺杂的高居里点BaTiO_3基PTCR陶瓷材料的室温电阻率且只有极少量的Mn~(2 )掺杂才使材料的PTC效应稍有提高。     

CVD synthesis of coal-gas-derived carbon nanotubes and nanocapsules containing magnetic iron carbide and oxide

Iron carbide-oxide filled carbon nanotubes and nanocapsules (CNCs) are separately synthesized by catalytic chemical vapor deposition of coal gas at 950 °C with ferrocene as catalyst. The products are examined using transmission electron microscopy and XRD techniques, showing that nanosized iron carbide-oxide particles are encapsulated by well ordered carbon layers. Magnetic moment measurement reveals that these carbon encapsulated iron carbide-oxides exhibit large magnetic coercivity at room temperature. It has been found that the filled CNCs are corrosion-proof and stable in hydrochloric acid. The effect and interaction between different gaseous components in the coal-gas during the formation of magnetic iron carbide-oxide filled carbon nanostructures are discussed.     

Suppression of inherent ferromagnetism in Pr-doped CeO(2) nanocrystals

Ce(1-x)Pr(x)O(2-δ) (0 ≤x≤ 0.4) nanocrystals were synthesized by self-propagating method and thoroughly characterized using X-ray diffraction, Raman and X-ray photoelectron spectroscopy and magnetic measurements. Undoped CeO(2) nanocrystals exhibited intrinsic ferromagnetism at room temperature. Despite the increased concentration of oxygen vacancies in doped samples, our results showed that ferromagnetic ordering rapidly degrades with Pr doping. The suppression of ferromagnetism can be explained in terms of the different dopant valence state, the different nature of the vacancies formed in Pr-doped samples and their ability/disability to establish the ferromagnetic ordering.     

Mechanism-based tuning of room-temperature ferromagnetism in Mn-doped β-Ga2O3 by annealing atmosphere

Mn-doped β-Ga₂O₃ (GMO) films with room-temperature ferromagnetism (RTFM) are synthesized by polymer-assisted deposition, and the effects of annealing atmosphere (air or pure O₂ gas) on their structures and physical properties are investigated. The characterizations show that the concentrations of vacancy defects and Mn dopants in various valence states and lattice constants of the samples are all modulated by the annealing atmosphere. Notably, the samples annealed in air (GMO–air) exhibit a saturation magnetization as strong as 170% times that of the samples annealed in pure O₂ gas (GMO–O₂), which can be quantitatively explained by oxygen vacancy (V_O)-controlled ferromagnetism due to bound magnetic polarons established between delocalized hydrogenic electrons of V_Os and local magnetic moments of Mn²⁺, Mn³⁺, and Mn⁴⁺ ions in the samples. Our results provide insights into mechanism-based tuning of RTFM in Ga₂O₃ and may be useful for design, fabrication, and application of related spintronic materials.     

Photocatalytic degradation of benzene,toluene, ethylbenzene,and xylene (BTEX) using transition metal-doped titanium dioxide immobilized on fiberglass cloth

Transition metal (Fe, V and W)-doped TiO₂ was synthesized via the solvothermal technique and immobilized onto fiberglass cloth (FGC) for uses in photocatalytic decomposition of gaseous volatile organic compounds—benzene, toluene, ethylbenzene and xylene (BTEX)—under visible light. Results were compared to that of the standard commercial pure TiO₂ (P25) coated FGC. All doped samples exhibit higher visible light catalytic activity than the pure TiO₂. The V-doped sample shows the highest photocatalytic activity followed by the W- and Fe-doped samples. The UV-Vis diffuse reflectance spectra reveal that the V-doped sample has the highest visible light absorption followed by the W- and Fe-doped samples. The X-ray diffraction (XRD) patterns indicate that all doped samples contain both anatase and rutile phases with the majority (>80%) being anatase. No new peaks associated with dopant oxides can be observed, suggesting that the transition metal (TM) dopants are well mixed into the TiO₂ lattice, or are below the detection limit of the XRD. The X-ray absorption near-edge structure spectra of the Ti K-edge transition indicate that most Ti ions are in a tetravalent state with octahedral coordination, but with increased lattice distortion from Fe- to V- and W-doped samples. Our results show that the TM-doped TiO₂ were successfully synthesized and immobilized onto flexible fiberglass cloth suitable for treatment of gaseous organic pollutants under visible light.     

Defect induced magnetic transition in Co doped CeO2 sputtered thin films

Cobalt-doped cerium dioxide thin films exhibit room temperature ferromagnetism due to high oxygen mobility in doped CeO₂ lattice. CeO₂ is an excellent doping matrix as there is a possibility of it losing oxygen while retaining its structure. This leads to increased oxygen mobility within the fluorite CeO₂ lattice, leading to formation of Ce³⁺ and Ce⁴⁺ species. Magnetic ceria materials are important in several applications from magnetic data storage devices to magnetically recoverable catalysts. In this paper, the room temperature ferromagnetism of rf sputtered Co doped CeO₂ thin films is reported whereas undoped CeO₂ thin films exhibit paramagnetic behavior. The ferromagnetic properties of the Co doped films were explained based on oxygen vacancies created by Co ions in Ce sites. This is further supported by X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and Raman. Change in surface morphology due to Co doping of the samples were analyzed using atomic force microscopy (AFM).     

Raman spectra,photoluminescence and ferromagnetism of pure,Co and Fe doped SnO2 nanoparticles

The pure and transition metal (Co and Fe = 3 and 5 mol%) doped SnO₂ nanoparticles have been synthesized by a chemical route using polyvinyl alcohol as surfactant. These nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman, Fourier transform infrared (FTIR) spectroscopy, photoluminescence (PL) and magnetic measurements. The XRD patterns show that all the samples have tetragonal rutile structure without any extra phase and the value of average particle size using FWHM lies within 12–29 nm is also confirmed by TEM. FTIR spectrum has been used to confirm the formation of SnO bond. Raman spectroscopy shows the intensity loss of classical cassiterite SnO₂ vibration lines which is an indication of significant structural modifications. From PL, an intense blue luminescence centered at a wavelength ～530 nm is observed in the prepared SnO₂ nanoparticles, which is different from the yellow-red light emission observed in SnO₂ nanostructures prepared by other methods. The strong blue luminescence from the as-grown SnO₂ nanoparticles is attributed to oxygen-related defects that have been introduced during the growth process. These Co and Fe-doped SnO₂ nanoparticles exhibit room temperature ferromagnetism and the value of their magnetic moment and phase transition temperature are sensitive to their size and stoichiometric ratio.     

Effect of Mn2+ and Cu2+ co-doping on structural and luminescent properties of ZnS nanoparticles

Undoped and transition metal (Cu, Mn, Cu:Mn) doped ZnS nanoparticles are synthesized by chemical co-precipitation method via an aqueous synthesis route. Synthesized samples are characterized by various techniques for their structural and optical properties. Crystallite size obtained from X-Ray Diffraction (XRD) is 1.68, 1.87, 1.50, 1.42 nm for undoped, Cu, Mn, Cu:Mn doped ZnS nanoparticles. The XRD, High Resolution Transmission Electron Microscopy, and Selected Area Electron Diffraction confirm the evolution of stable hexagonal phase of ZnS nanoparticles at low temperature. Energy Dispersive Spectroscopy confirms the doping of nanoparticles. Blue shift in UV absorbance shows the increase in optical bandgap with decrease in particle size. The Photoluminescence studies exhibit blue, yellow and red emission in visible region. Surface functionalization of nanoparticles is confirmed from Fourier Transform Infra Red spectroscopy. The present samples are tunable in wider range of emission and are prospective candidates for biological labels due to their fluorescent properties.     

Proteic sol-gel synthesis,structure and magnetic properties of Ni/NiO core-shell powders

Core-shell structured magnetic Ni/NiO powders were prepared by a proteic sol-gel route. Commercial gelatin and nickel nitrate were used as precursor materials. The synthesized material was calcined in air at 500 °C and further investigated by XRD, VSM and TEM. In order to investigate the effects of the structure on the magnetic properties, NiO powders were synthesized by three other methods for sake of comparison: citrate method, nitrate calcination and combustion method. XRD results revealed that the core-shell structured material is composed of 84.8 wt% NiO and 15.2 wt% Ni, while the samples from other methods are single phase. Hysteresis loop at room temperature showed a strong ferromagnetic behavior for samples prepared by proteic sol-gel and citrate methods. Powders from nitrate calcination and combustion showed weak ferromagnetic behavior most likely attributed to unpaired moments in their nanoparticles. The overall results showed that the proteic sol-gel method is a versatile chemical way to prepare Ni/NiO core-shell powders with high ferromagnetic signals.     

Sonochemical synthesis of CoFe2O4 nanoparticles and their application in magnetic polystyrene nanocomposites

CoFe₂O₄ (CoFe) nanoparticles were synthesized via a facile surfactant-free sonochemical reaction. For preparation of magnetic polymeric films, CoFe₂O₄ nanoparticles were added to polystyrene (PS). Nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Magnetic properties of the samples were investigated using an alternating gradient force magnetometer (AGFM). CoFe₂O₄ nanoparticles exhibit a ferromagnetic behaviour with a saturation magnetization of 62 emu/g and a coercivity of 640 Oe at room temperature. By preparing magnetic films the coercivity is increased. The coercivity of PS/CoFe₂O₄ (10%) nanocomposites is higher than that obtained for PS/CoFe₂O₄ (30%).