Increasing Fe Doping Research Articles

Premartensite serving as an intermediary state between strain glass and martensite in ferromagnetic Ni-Fe-Mn-Ga

Previous investigations indicate that the two intrinsically different states, i.e., strain glass and premartensite in ferromagnetic Ni-Mn-Ga based system share some similarities in their transforming properties, such as nano-domain structure, elastic anomaly and temperature-induced transition to martensite. This indicates that the two states are possibly related with each other. However, the relationship between them is unclear so far. To explore this problem, we investigated the transforming behaviors of the ferromagnetic Ni55-xFexMn20Ga25 (x = 4–14) system. It was found that the transforming route of this system changes greatly with increasing Fe content. We also observed that the strain glass transforms into premartensitic state upon cooling, which is called spontaneous strain glass to premartensite transition. The local structure of strain glass is similar to that of premartensite. Moreover, a strain glass phase diagram of the Ni-Fe-Mn-Ga system was constructed, which reveals that the premartensite serves as an intermediary state between strain glass and martensite. With increasing Fe doping, the system changes from the martensite (long-range-ordered strain state with large spontaneous strain) into the premartensite (long-range-ordered strain state with small spontaneous strain) at first, and then the strain glass (short-range-ordered strain state with small local strain) is derived from premartensite by further doping Fe.

Effect of Fe doping on structural, magnetic, and electrical properties of non-magnetic and magnetic rare earth-based perovskite chromites La0.5Nd0.5Cr1-x Fe x O3 (0 ≤ x ≤ 1)

The structural, magnetic, and electrical properties of new series La0.5Nd0.5Cr1-x Fe x O3 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) have been reported. All the phases crystallize in the orthorhombic symmetry with Pbnm space group. The unit cell volume of La0.5Nd0.5Cr1-x Fe x O3 increases monotonically with increasing Fe doping. Magnetization studies showed that all our investigated phases (except x = 0.8 and 1.0) exhibit a paramagnetic–anti-ferromagnetic transition at low temperature. The variation in Neel temperature (T N) with increasing x can be explained in terms of magnetic interactions due to Fe doping. Irreversibility between the zero-field-cooled (ZFC) and field-cooled (FC) magnetization is clearly seen close to T N. All the phases show that insulating behavior and the transport properties are dominated by the polaron hopping mechanism with increase in polaron hopping energy with Fe content.

Investigations of structural, optical, and photovoltaic properties of Fe-alloyed ZnS quantum dots

Pure ZnS and Fe-alloyed ZnS quantum dots (QDs) prepared by wet-chemical method at room temperature using mercaptoethanol as a capping agent. The nominal concentrations of Fe were 5, 10, and 15% weight of Fe. The QDs were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis of X-rays (EDAX), optical absorption and photoluminescence (PL) measurements. The cubic phase of pure and Fe-alloyed ZnS QDs was indicated using the XRD measurements. It was determined that the sizes of doped samples decrease as the Fe concentrations are increased. The band gaps of QDs were investigated using optical measurements. It was observed that the band gaps and the absorption windows of Fe-alloyed ZnS QDs increase with the increase in the concentrations of Fe. It was seen that as the concentration of Fe increases, both the absorption and the emission peaks of the alloyed ZnS QDs shift to shorter wavelength. The photovoltaic properties of Fe alloyed ZnS QDs have been investigated in this study for the first time. The pure ZnS and Fe-alloyed ZnS QDs were used to make quantum dots-sensitized solar cells. The performances of the solar cells, with the short circuit current density (JSC) and open circuit voltage (VOC) and incident photon to electron conversion efficiency (IPCE) of Fe-alloyed ZnS QDs increased with increasing Fe doping. Thus, Fe-alloyed ZnS QDs can be used as promising materials in solar cell technology due to fact that they have wider optical absorption spectrums.

Magnetic Phase Separation in Diluted Magnetic System: Zn1−x Fe x O

Single-phase diluted magnetic systems Zn1−x Fe x O have been prepared by chemical route. Structural and spectroscopic (UV–Vis and Mössbauer) studies indicate the incorporation of Fe3+ ions in the lattice sites. The UV–Vis results point to a systematic increase in the band gap with increasing Fe doping. The room temperature magnetization of Zn1−x Fe x O indicates a paramagnetic behavior which is in accordance with the Mössbauer results, illustrating quadrupolar doublet. At low temperature, the zero-field-cooled (ZFC) magnetization shows a cusp and this temperature increases systematically with decreasing particle size. The weak exchange bias effect manifested by a M–H loop shift is observed for x = 0.03. This shift is accompanied by the enhancement of coercivity. The dc magnetization results suggest the coexistence of ferromagnetic and antiferromagnetic exchange interactions for low doping of Fe, i.e., for x = 0.03.

Effect of Fe-doping on the structural, optical and magnetic properties of ZnO nanostructures synthesised by co-precipitation method

Nanoparticles of Zn1−xFexO (0≤x≤0.2) were prepared by co-precipitation method followed by drying at 200°C. Tween-80, a non-ionic surfactant, not reported in earlier studies was used during preparation process. X-ray diffraction analysis showed the formation of wurtzite ZnO phase nanostructures. The Rietveld analysis confirmed the formation of hexagonal wurtzite structure for all dopant levels without any impurity. Morphological observations using scanning electron microscopy show the formation of nanoparticles with remarkable morphologies. Photoluminescence spectra revealed emission bands in both UV and visible regions due to the defect centres acting as trap levels. Optical studies carried out by diffuse reflectance spectroscopy (DRS) indicated a decrease in the value of the band gap with increasing Fe doping concentration. The elemental composition of Zn, Fe and O quantitatively obtained from EDAX analysis confirmed the purity of the as-prepared nanopowders and that the chemical composition is close to the starting stoichiometries. Magnetization–Field (M–H) hysteresis curves revealed the appearance of ferromagnetic behaviour, where the magnetic characteristics such as coercivity and saturation magnetization values, were found to be sensitive to Fe doping level.

Chemical spray pyrolysis deposition of transparent and conducting Fe doped CdO thin films for ethanol sensor

Transparent conducting cadmium oxide (CdO) and Fe (0.5, 1, 1.5 and 2wt%) doped CdO thin films were deposited on glass substrate using facile chemical spray pyrolysis technique. The influence of Fe doping on the structural, morphological, optical and electrical properties of CdO thin films were systematically investigated using different characterization techniques such as X-ray diffraction (XRD), atomic force microscope (AFM), UV–vis transmittance and Hall measurement respectively. The XRD patterns clearly reveal the pure and Fe doped CdO films are polycrystalline nature along with cubic crystal structure. AFM images show the roughness of the CdO thin film decreases with respect to Fe doping concentration. The surface structure of the 1wt% Fe doped CdO film was investigated by X-ray photoelectron spectroscopy (XPS). Optical transmittance of the CdO thin film decreases with increasing of Fe doping concentration. The optical band gap value of the CdO thin film gradually decreases from 2.61 to 2.18eV with increasing Fe doping concentration. From Hall measurement, the minimum value of resistivity is obtained for (7.67×10−4Ωcm) 1wt% of Fe doped CdO thin film. Finally, the ethanol sensor behaviour was observed using home-built sensor unit. The maximum ethanol gas response of 56.12% is observed for 1wt% of Fe doped CdO thin films. This result suggests the Fe doped CdO is one of the promising material in sensor applications.

Fe-Doped TiO2 Thin Films for CO Gas Sensing

Fe-doped TiO2 thin films were prepared by the sol–gel technique on silicon substrate. The thin films were evaluated for detection of carbon monoxide (CO) gas at room temperature. The TiO2 films were characterized by x-ray diffraction (XRD) analysis, field-emission scanning electron microscopy, and ultraviolet–visible (UV) spectroscopy. The characterization revealed that, as the doping concentration was increased, the grain size decreased. XRD patterns revealed the phase transition from rutile to anatase with addition of different percentages (weight/volume) of Fe. The bandgap determined from UV spectroscopy was found to decrease with increasing Fe doping concentration. Fe doping was observed to have a significant effect on the resistivity of the doped TiO2 thin films. The gas sensing behavior of the films was studied by exposure to different concentrations of CO gas with measurement of the electrical resistance. It was observed that Fe-doped (7% weight/volume) TiO2 exhibited high sensitivity and good response/recovery on exposure to CO gas in the concentration range from 100 ppm to 900 ppm in Ar.

Preparation, Infrared Emissivity, and Dielectric and Microwave Absorption Properties of Fe-Doped ZnO Powder

Fe-doped ZnO powders have been synthesized by the coprecipitation method using zinc nitrate [Zn(NO3)2·6H2O] as starting material, urea [CO(NH2)2] as precipitator, and ferric nitrate [Fe(NO3)3·9H2O] as doping source. The microstructure of the prepared powders has been characterized by x-ray diffraction and scanning electron microscopy. Results show that, when the molar ratio of Fe to (Zn + Fe) was less than 0.09, the prepared powder was ZnO(Fe) solid solution, and the ZnFe2O4 impurity phase appeared when the Fe doping content was further increased. The electric permittivity in the frequency range of 8.2 GHz to 12.4 GHz and the average infrared emissivity in the wavelength range of 8 μm to 14 μm have been determined for the prepared powders. The average infrared emissivity decreased with increasing Fe doping content. The real (e′) and imaginary part (e″) of the permittivity of the prepared powders showed opposite trends. When the molar ratio of Fe to (Zn + Fe) was 0.03, the prepared Fe-doped ZnO powder demonstrated the best microwave absorption in the frequency range of 8.2 GHz to 12.4 GHz.

Structural, elemental, optical and magnetic study of Fe doped ZnO and impurity phase formation

We have prepared a series of (ZnO)1−x(Fe2O3)x≤0.10 bulk samples with various concentrations of Fe dopant by ball milling and investigated their structural, compositional, optical and magnetic properties by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectrometer and vibrating sample magnetometer (VSM), respectively. Information about different impurity phases was obtained through Rietveld refinements of XRD data analysis. XPS results showed different valence states (Fe2+ and Fe3+) supported by shaking satellite peaks in samples. With increasing Fe doping percentage, the crystal quality deteriorated and a shift of E2 low band (characteristic of ZnO) has been observed in Raman spectra. Energy band gap estimated from reflectance UV–vis spectroscopy showed shift for all bulk samples. The magnetic behavior was examined using a vibrating sample magnetometer (VSM), indicating ferromagnetic behavior at room temperature (300K). The effective magnetic moment per Fe atom decreases with increase in doping percentage which indicates that ferromagnetic behavior arises from the substitution of Fe ions in the ZnO lattice.

Dopant spin states and magnetism of Sn1−xFexO2 nanoparticles

This work reports detailed investigations of a series of ∼2.6 nm sized, Sn1−xFexO2 crystallites with x = 0–0.10 using Mossbauer spectroscopy, x-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectroscopy (EPR), and magnetometry to determine the oxidation state of Fe dopants and their role in the observed magnetic properties. The magnetic moment per Fe ion μ was the largest ∼6.48 × 10−3 μB for the sample with the lowest (0.001%) Fe doping, and it showed a rapid downward trend with increasing Fe doping. Majority of the Fe ions are in 3+ oxidation state occupying octahedral sites. Another significant fraction of Fe dopant ions is in 4+ oxidation state and a still smaller fraction might be existing as Fe2+ ions, both occupying distorted sites, presumably in the surface regions of the nanocrystals, near oxygen vacancies. These studies also suggest that the observed magnetism is not due to exchange coupling between Fe3+ spins. A more probable role for the multi-valent Fe ions may be to act as charge reservoirs, leading to charge transfer ferromagnetism.

About the defect structure in differently doped PZT ceramics: A temperature dependent positron lifetime study

Pure and doped PZT ceramics (PZT:La+Fe, PZT:La, PZT:Gd, PIC 151 and with 0.1, 0.25, 0.5, 1.0mol% Fe doped samples) have been examined by Positron Annihilation Lifetime Spectroscopy (PALS) in the range of temperatures between 150 and 375K. It was found that the defect-related lifetime increased with increasing temperature, indicating vacancy-like defects. With increasing Fe doping, a loss of vacancy agglomerations was observed, as well as a weaker dependence of lifetime on temperature.

Study of structural and optical properties of iron doped ZnO thin films prepared by sol-gel

Fe doped ZnO thin films with various levels of iron doping concentration (0, 1, 2, 3 at.%) content were produced by sol-gel dip coating method. The influence of Fe doping on the structural, morphological and optical properties of ZnO thin films was investigated. X-ray diffraction has shown that the films are polycrystalline and textured with the hexagonal structure. Scanning electron microscope has indicated that crystallites dispersion in the films is generally homogeneous and the particle morphology changes with increase in the doping concentration. FTIR measurements show that the intensity of Zn-O band increases with increasing doping concentration and the UV-visible transmittance results show a high transparency in the visible range. The room temperature photoluminescence (PL) spectra of Fe doped ZnO indicate that the green-orange emission decrease with increasing Fe doping.

Reduced Three-Dimensional (3D) Conductivity in Fe Doped CuTl-1223 Superconductors

The excess conductivity of Fe doped Cu0:5Tl0:5Ba2Ca2Cu3-yFeyO10-δ, with y = 0, 0.02, 0.03, 0.05, 0.075 samples is investigated for comparison of the dimensionality of fluctuations above the mean-field critical temperature. It is observed from these studies that at lower temperatures (close to the transition temperature), the fluctuation in the order parameter of the carriers follows a three dimensional (3D) behavior, whereas at high temperature it follows a two dimensional (2D) behavior. From the analysis of our results, we evaluated the exponents, the coherence length, the crossover temperature, and inter-layer coupling strength (J) of the Fe doped and undoped samples. This striking linear depression of Tc (R = 0) and the magnitude of diamagnetism can be correlated with the decreased width of the 3D and 2D regimes with increased Fe concentrations. The crossover temperature from 2D to 3D has substantially been shifted to a lower temperature with increasing Fe doping, which may possibly be due to an enhanced interaction of the ferromagnetic spin of Fe^(+3) with the mobile free carriers in the CuO2 planes, this scattering also promotes a reduction in the coherence length of the carriers along the c-axis.

Ferromagnetic Behaviors in Fe‐Doped NiO Nanofibers Synthesized by Electrospinning Method

Ni1−xFexO nanofibers with different Fe doping concentration have been synthesized by electrospinning method. An analysis of the phase composition and microstructure shows that Fe doping has no influence on the crystal structure and morphology of NiO nanofibers, which reveals that the doped Fe ions have been incorporated into the NiO host lattice. Pure NiO without Fe doping is antiferromagnetic, yet all the Fe‐doped NiO nanofiber samples show obvious room‐temperature ferromagnetic properties. The saturation magnetization of the nanofibers can be enhanced with increasing Fe doping concentration, which can be ascribed to the double exchange mechanism through the doped Fe ions and free charge carriers. In addition, it was found that the diameter of nanofibers has significant impact on the ferromagnetic properties, which was discussed in detail.

Room-temperature ferromagnetism of Fe-doped TiO2 nanoparticles driven by oxygen vacancy

A series of Ti1−xFexO2−δ (0≤x≤0.03) nanoparticles (NPs) were synthesized by sol–gel route. The NPs had a size distribution in the range of 15–40nm and were identified as the anatase TiO2 by X-ray diffraction (XRD) and Raman analysis. XRD, selected area electron diffraction, Raman and Mössbauer analysis ruled out the signature of Fe-cluster or any other oxides of Fe. The redshifting of the band edge emission peak observed in UV–vis absorption studies further confirmed the doping of Fe ions in the TiO2 lattice. Raman studies show the shifting and broadening in Eg(1) and Eg(3) modes with Fe doping. It suggested that the activation of ferromagnetism with increasing Fe doping concentration was related to the oxygen vacancy defects. The presence of such defects was further confirmed from electron paramagnetic resonance (EPR) measurements. The observed ferromagnetism is interpreted in terms of bound magnetic polaron (BMP) model.

The effect of Fe doping on structural and magnetic properties of nanocrystallite Co2Cr1−xFexAl Heusler alloys prepared by mechanical alloying

Mechanical alloying has been used to produce nanocrystallite Co2Cr1−xFexAl (x = 0, 0.4, 0.6, 1) Heusler alloys. The formation of the L21 phase of Co2Cr1−xFexAl by the mechanical alloying method was investigated. The effect of Fe doping on the structural and magnetic properties of the samples was also studied. The results were compared with the Slater Pauling prediction. A comparison between these samples and those prepared by the arc-melting method in the literature was made. An increase of the coercivity Hc with the increasing Fe doping level was observed. This phenomenon was explained by the increases of lattice strain and magnetic anisotropy with the increasing Fe content.

Influence of the Jahn—Teller distortion on magnetic ordering in TbMn1−xFexO3

The Jahn—Teller distortion plays an important role in determining the exchange interaction in rare-earth manganites. In this work we study the influence of the Jahn—Teller distortion on the magnetic structures of TbMn1−xFexO3 (x = 0, 0.02, 0.05, 0.10, and 0.20) single crystals in the basal MnO2 plane. The decrease in the quadruple splitting with the increasing Fe doping indicates the reduction of the Jahn—Teller distortion, which makes the nearest neighboring (NN) FM interaction dominant over the next nearest neighbor (NNN) AFM interaction. This alteration is favorable for the development of A-type AFM ordering instead of the spiral magnetic ordering, which collapses when x ≥ 0.05. The analysis of dielectric data indicates that the ferroelectricity is arising from the peculiar spiral magnetic ordering.

Synthesis and Characterization of Fe-Doped CdSe Nanoparticles as Dilute Magnetic Semiconductor

Cd1−x Fe x Se (0≤x≤0.1) nanoparticles were synthesized by hydrothermal method. The solubility limit of Fe in CdSe nanoparticles was found to be less than 6 % as obtained from X-ray diffraction (XRD) study. With the increase in doping concentration at and above it, secondary phase of FeSe2 starts appearing. The presence of Cd, Se, and Fe has been confirmed by energy dispersive X-ray spectroscopy (EDS). The increase in band gap value has been confirmed by UV-visible spectra and the variation in emission intensity of photoluminescence (PL) measurements further indicates the incorporation of Fe in CdSe nanoparticles. Transmission electron microscopy (TEM) reveals the spherical nature of synthesized nanoparticles, and the particle size decreases with increasing Fe doping concentration. Fourier transform Infrared spectra (FTIR) confirm the capping of sodium dodecyl sulfate (SDS) surfactant on pure and Fe-doped CdSe nanoparticles. The synthesized nanoparticles show room-temperature ferromagnetic behavior, and the saturation magnetization value was found to increase with Fe doping concentration.

Some physical properties and Vickers hardness measurements of Fe diffusion-doped Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy superconductors

In this study we have investigated the influence of iron diffusion and diffusion-annealing time on the mechanical and the superconducting properties of bulk Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy superconductors by performing X-ray diffraction (XRD), scanning electron microscopy (SEM), Vickers hardness, dc resistivity (ρ-T) and critical current density (Jc) measurements. The samples are prepared by the conventional solid-state reaction method. Doping of Bi-2223 was carried out by means of iron diffusion during sintering from an evaporated iron film on pellets. Then, the Fe layered superconducting samples were annealed at 830 °C for 10, 30 and 60 h. The mechanical properties of the compounds have been investigated by measuring the Vickers hardness (Hv). The mechanical properties of the samples were found to be load dependent. The load independent Vickers hardness (H0), Young’s modulus (E), yield strength (Y), and fracture toughness (KIC) values of the samples are calculated. These all measurements showed that the values of the Vickers hardness, critical current density, and critical transition temperature and lattice parameter c increased with increasing Fe doping and diffusion-annealing time.

Visible light active Fe doped TiO2 nanowires grown on graphene using supercritical CO2

Visible light driven TiO2 photocatalyst nanowire arrays doped with Fe were grown on the surface of functionalized graphene sheets (FGSs) using a sol–gel method in the green solvent, supercritical carbon dioxide (scCO2). The morphology of the synthesized catalysts was studied by SEM and TEM, which showed uniform formation of Fe doped TiO2 nanowires on the surface of the graphene sheets, which acted as a template for nanowire growth through surface –COOH functionalities. Increasing Fe content in the nanowires gave only small changes in morphology but significantly higher BET surface areas. Optical properties of the synthesized composites were examined by UV and PL spectroscopy which showed a significant reduction in band gap with increasing Fe content, i.e. decreasing from 3.2 to 2.3eV at 0.6% Fe. High resolution XPS and Raman analysis showed the interaction of Fe with the TiO2 lattice and also bonding of TiO2 with –COOH groups on the surface of the graphene sheets. The photocatalytic properties of the prepared catalysts were evaluated under visible light solar irradiation for the photodegradation of 17β-estradiol (E2), an endocrine disrupting hormone which is commonly released into aquatic environments. All prepared catalysts with different ratios of Fe were active in the visible region of the solar spectrum with the photocatalytic activity significantly enhanced with increasing Fe doping levels with a plateau at 0.6–0.8% Fe. The prepared catalysts showed higher activity than both Fe doped TiO2 and TiO2/FGSs composites.