EPR Spectra Of Fe3 Research Articles

Enhanced magnetic properties of Fe3+ doped ZnS nanocrystals via low temperature co-precipitation: spintronic and nano-device applications

The present work emphasises synthesis and characterization of undoped and Fe3+ doped ZnS nanocrystals. The prepared samples are synthesized by simple co-precipitation technique. The recorded XRD pattern confirms the cubic structure of prepared samples and its estimated average crystallite size is 3–3.5 nm range, and also evaluated micro-structural parameters. SEM images of prepared samples exhibit granular structure with spherical particles and non uniform in shape, size where as Fe3+ doped sample is more agglomerated. TEM images of undoped sample depicted rod like structures where as Fe3+ doped sample exhibits spherical shaped structures. The energy bands obtained in UV–vis region from optical absorption spectrum are recognized as characterstic bands of Fe3+ ions and also evaluated the crystal field, inter electronic parameters (Dq, B and C). EPR spectrum of Fe3+ doped sample exhibited a strong signal at g = 2.136. Photoluminescence spectrum of undoped sample is witnessed by strong blue emission band at 421 nm where as Fe3+ doped ZnS has an additional weak peak observed at 609 nm (4T2 → 6A1). The evaluated CCT values are 2568 K for ZnS and 3079 K for Fe3+ doped ZnS. VSM analysis reveals the observation of enhanced magnetism for Fe3+ doped ZnS nanocrystals compared to undoped sample ZnS. Thermal analysis signifies that the prepared samples are stable upto 888 °C (ZnS) and 993 °C (Fe3+ doped ZnS). The prepared materials may suitable for the various device applications in nanoscale magnetic, optical-spintronic devices and led to fabricate DMS materials for new trending applications.

Sonochemical assisted synthesis and spectroscopic characterization of Fe3+ doped ZnO diluted magnetic semiconductor

Fe3+ doped ZnO nanopowder has been synthesized by sonochemical assistance and characterized by different spectroscopic techniques. The structure, surface morphologies and optical properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence spectrometer (PL) and ultraviolet–visible spectrophotometer. XRD reveals that Fe3+ ions enter into ZnO lattices without any secondary phases. SEM micrographs of prepared sample show that surface is rough and stone like structure with different sizes. PL studies of Fe3+ doped ZnO nanopowder exhibits ultraviolet and blue emission bands. Magnetometric measurements (vibrating sample magnetometer) indicate ferromagnetic behavior at room temperature. This observation is further confirmed by the EPR spectrum of Fe3+ doped ZnO at room temperature.

Synthesis, EPR and luminescent properties of YAlO3:Fe3+ (0.1–0.9 mol%) nanopowders

A simple and inexpensive combustion method was used to prepare Fe3+ doped YAlO3 perovskite within few minutes at low temperature (400±10°C). This might be useful in lowering the cost of the material. The final products were well characterized by various spectroscopic techniques such as PXRD, SEM, TEM, FTIR and UV–Visible. The average crystallite size was estimated from the broadening of the PXRD peaks and found to be in the range 45–90nm, the results were in good agreement with the W–H plots and TEM. The crystallites show dumbbell shape, agglomerated particles with different size. The TL glow curves of 1–5kGy γ-irradiated YAlO3:Fe3+ (0.1mol%) nanopowder warmed at a heating rate of 3°Cs−1 records a single glow peak at ∼260°C. The kinetic parameters namely activation energy (E), order of kinetics (b) and frequency factor (s) were determined at different gamma doses using the Chens glow peak shape method and the results were discussed in detail. The photoluminescence spectra for Fe3+ (0.1–0.9mol%) doped YAlO3 records the lower energy band at 720nm (4T1 (4G)→6A1 (6S)) and the intermediate band located at 620nm (4T2 (4G)→6A1 (6S)) with the excitation of 378nm. The higher energy band located at 514nm was associated to 4E+4A1 (4G)→6A1 (6S) transition. The resonance signals at g values 7.6, 4.97, 4.10, 2.94, 2.33 and 1.98 were observed in EPR spectra of Fe3+ (0.1–0.9mol%) doped YAlO3 recorded at room temperature. The g values indicate that the iron ions were in trivalent state and distorted octahedral site symmetry was observed.

Specific features of the substitution of Fe3+ impurity ions for Zr4+ in NaZr2(PO4)3 single crystals

The EPR spectra of Fe3+ impurity ions in NaZr2(PO4)3 single crystals at 300 K are investigated, and the spin Hamiltonian of these ions is determined. A comparative analysis of the spin-Hamiltonian and crystal-field tensors is performed using the maximum invariant component method. It is demonstrated that Fe3+ impurity ions substitute for Zr4+ ions with local compensator ions located in cavities of the B type. It is revealed that the invariant of the spin-Hamiltonian tensor B4 and the crystal-field tensor V444 depend substantially on the mutual arrangement of ions in the first and second coordination spheres. The corresponding dependences are analyzed.

Manifestation of noncentrality in the EPR spectrum of Fe3+ in polycrystalline substances

The EPR spectrum of an impurity Fe3+ ion in three organic substances is investigated in the temperature range 4.2–295 K: bromocresol green (C21H14Br4O5S), crystal violet (C25H30ClN3), and a compound of crystal violet with fullarene ((C25H30ClN3)+C60). An unusual change in the shape of the EPR spectrum as a function of temperature is observed in all substances investigated. At 4.2 K the spectrum is a superposition of three contributions: two resonance lines with effective g factors g1=4.39 and g2=2.03 and a nonresonance contribution. As the temperature changes, the intensities become redistributed between these three contributions. As temperature increases, the total intensity of line 1 and the nonresonance contribution decrease and the intensity of line 2 increases. The observed properties of the EPR spectra are characteristic for noncentral ions which possess a multiple-minimum potential. The redistribution of the populations of vibronic states of a noncentral Fe3+ ion determines the temperature variation of the EPR spectrum.

The effects of applied electric fields on the EPR spectra of Fe3+ ion in tetragonal SrTiO3 crystal

The electric-field-induced zero-field splittings for Fe3+ in tetragonal phase of SrTiO3 are studied from the microscopic mechanisms and the empirical superposition model. From the studies, it is found that the induced zero-field splittings can be reasonably explained by considering suitable Fe3+ displacements along the electric-field direction in the tetragonal (FeO6)9− groups in SrTiO3:Fe3+. The electric-field-induced Fe3+ displacements obtained by the above two methods are close to each other and they are also comparable with those obtained from the force-balance equation. The strong temperature dependences of electric-field-induced zero-field splitting and hence of Fe3+ displacement can be attributed mainly to the strong temperature dependence of dielectric constant of SrTiO3 crystal.

Identificationof iron in 6H-SiC crystals by electron paramagnetic resonance

We report on the first observation of the electron paramagnetic resonance of iron impurityin SiC:Fe crystals. Iron exists in the Fe3+ (3d5) charge state with electron spin S = 5/2and seems to occupy silicon sites in the 6H-SiC lattice.The EPR spectrum of Fe3+ in SiC shows a characteristic anisotropy of an S = 5/2 systemin a strong axial crystalline field with fine structure parameter D = 0.25 cm-1.The g-factor is nearly isotropic, g = 1.99.The possibility of using iron doping to obtain semi-insulating SiC crystals is discussed.

EPR of trivalent iron ions in a LiCaAlF6 crystal

The orientational dependences of the EPR spectra of Fe3+-doped LiCaAlF6 single crystals (space group P31c, Z=2), grown at the Laboratory of Magnetic Radio Spectroscopy at Kazan’ State University, have been investigated in detail. The spectrum is described by a trigonal spin Hamiltonian with the following parameters: B 20=40.072×10−4 cm−1, B 40=−5.799×10−4 cm−1, B 43=−4.281×10−4 cm−1, A s=24.33±1, A p=6.13±1, g ∥=g ⊥=2.00217±0.0003. A theoretical calculation of the hyperfine structure parameters shows that they are described quite well when allowance is made for the overlapping of the wave functions of the paramagnetic center and the ligands (F−).

Determination of new sites for two Fe3+ EPR centres in KTiOPO4

EPR spectra of Fe3+ ions in single crystals of KTiOPO4 (KTP), synthesized by the flux method, have been investigated at room temperature by employing a Bruker Q-band spectrometer. From the angular dependence of the EPR spectra, two Fe3+ centres denoted as C1 and C2 have been identified, in agreement with the previous analysis by other investigators. In this study, for the first time we have fully identified two groups of four magnetically inequivalent Fe3+ sites each belonging to the centres C1 and C2. Two sets of triclinic spin-Hamiltonian parameters, which simultaneously fitted EPR data for the four sites belonging to the centres C1 and C2, were determined. The direction cosines of the principal axes of the g-tensor as well as the second-order zero-field splitting (ZFS) tensor are found to be given by the relations: lmn, lmn, lmn and lmn for each four Fe3+ sites of C1 as well as C2, respectively, consistent with the crystallographic point group mm2 of KTP.

EPR study of Fe3+ and Mn2+ in CeO2 and ThO2

Attempts were made to grow CeO2 and ThO2 single crystals doped with transition metal ions. Only Fe3+ and Mn2+ could be detected by the EPR technique. The EPR spectrum of Fe3+ in CeO2 exhibits the well-known fine structure in cubic fields. The parameters areg=2.0044(1) anda=15.6(1)·10−4 cm−1. The hyperfine constantA for57Fe in hexahedral coordination was found to be 8.9(1)·10−4 cm−1. The EPR spectrum of Mn2+ in CeO2 reveals two cubic Mn2+ centers. The parameters for center 1 areg=1.9999(1) andA=86.9(1)·10−4 cm−1 and for center 2g=1.9984(1) andA=87.0(1)·10−4 cm−1. Heating the Mn doped CeO2 samples in hydrogen, the Mn2+ centers transform from cubic into trigonal centers with approximate values ofg=1.9988(2),A=84.5(6)·10−4 cm−1 andD=203(1)·10−4 cm−1. The two observed Mn2+ centers in ThO2 exhibita priori axial symmetry with approximate values ofg=2.0006(2),A=88.9(4)·10−4 cm−1 andD=33(3)·10−4 cm−1.

EPR of Fe3+ in acetylacetonates

EPR spectra of Fe3+ in Al(acac)3 and Ga(acac)3 single crystals were measured in the temperature range between 20 K and room temperature. In the Al compound one center was found above 140 K and three below this temperature due to a phase transition. In Ga(acac)3 two centers with similar zero-field splitting parameters and orientations of their principal axes were observed in agreement with results for Cr3+. In all cases unusually large fourth-order zero-field splitting parameters for low symmetries were required for fitting and simulation of the angular dependences of the spectra. The results for the two compounds differed significantly. The orientations of the principal axes deviate considerably from those calculated from the crystal structure data by application of the superposition model. Thus like in the cases of Cr3+ in the same compounds and on Mn2+ in Zn(acac)2·H2O this model is not applicable, most likely due to delocalization of the conjugated π-electron systems of the ligands.

EPR parameter of order degree in natural kaolinite and its relation to weathering

In studying the degree of order (or disorder) in kaolinite, X-ray diffraction and DTA are commonly used, but spectroscopic method (as EPR, IR)has become a useful and additional tool now. The total iron content and the intensity of Fe3+(I) line are not always correlated negatively with order degree in natural kaolinite. But in the present case, they show direct correlations. So it appears that they cannot be used as an ideal parameter for measuring the order degree in kaolinite. The ratio of Fe3+(E)line and Fe3+(I)line intensities obtained directly from EPR spectrum of Fe3+at geff=4 appears to be a better EPR parameter for measuring the magnitude of order degree in kaolinite and for determining the intensity of some geological processes (such as weathering, hydrothermal alteration and so on) with aid of kaolinite. However, EPR data can only be used to qualitatively estimate the degree of order in kaolinite and related geological process for the present. There is still much work to be done in order to make EPR a method of quantitative estimation in the field.

Characterization of the cycle of iron-mediated electron transfer from Adriamycin to molecular oxygen.

The anticancer drug adriamycin binds iron and these complexes cycle to reduce molecular oxygen (Zweier, J. L. (1984) J. Biol. Chem. 259, 6056-6058). Optical absorption, EPR, and Mössbauer spectroscopic data are correlated with polarographic O2 consumption and chemical Fe2+ extraction measurements in order to characterize each step in this cycle. Fe3+ binds to adriamycin at physiologic pH forming a complex with an optical absorbance maximum at 600 nm. EPR signals at g = 4.2 and g = 2.01, and a doublet Mössbauer spectrum with isomer shift delta = 0.57 mm/s and quadrupole splitting delta EQ = 0.74 mm/s are observed indicating that the Fe3+ bound to adriamycin is high spin S = 5/2. Under anaerobic conditions the absorbance maximum at 600 nm decreases with an exponential decay constant = 0.77 h-1, and the EPR and Mössbauer spectra of Fe3+-adriamycin similarly decrease as the Fe3+ is reduced to EPR silent Fe2+. The Fe2+-adriamycin complex which is formed exhibits a Mössbauer spectrum with delta = 1.18 mm/s and delta EQ = 1.82 mm/s indicative of high spin Fe2+. As the EPR spectra of Fe3+-adriamycin decrease on reduction of the Fe3+ to Fe2+ a signal of the oxidized adriamycin free radical appears at g = 2.004 with line width of 8 G. On exposure to O2 the absorption maximum at 600 nm, the Fe3+ EPR, and the Fe3+ Mössbauer spectra all return. Polarographic measurements demonstrate that O2 is consumed and that H2O2 is formed. Addition of high affinity Fe2+ chelators block O2 consumption indicating that Fe2+ formation is essential for O2 reduction. This cycle of iron-mediated O2 reduction can explain the formation of the reactive reduced oxygen and adriamycin radicals which are thought to mediate the biological activity of adriamycin.

Le fer dans les kaolins. Étude par spectrométries RPE, Mössbauer, EXAFS

Seven kaolins were examined. Several phases containing iron were analysed by comparison of the used spectroscopies. Mössbauer spectroscopy shows that a part of the Fe²⁺ cannot be in the structure of kaolinite. At low temperature, we observe for one sample, presence of superparamagnetic particles of hematite and goethite. For the others we detect it only a little, this implies either their quantities are low or particule sizes are very thin (<20 Å). EPR spectrum of Fe³⁺ consists in two parts : — One attributed to a distribution of the sites of isolated Fe³⁺ with variable symmetries. — The second gives a wide line attributed to superparamagnetic phases. We make semi-quantitative the analysis of this wide line by comparison with the other spectroscopies. For example, EXAFS spectroscopy shows for one sample that all the iron atoms belong amorphous structure, this is possible only in a subsidiary phase of the clay. With these results, we can say that the majority of iron is in phases associated with kaolinite.

Epr spectra of Fe3+ and Cr3+ in powdered rutile

Epr spectra of Fe3+ and Cr3+ in powdered rutile

NMR and EPR studies of the chemically intermediate plagioclase feldspars

The NMR spectra of 27Al and 23Na and the EPR spectra of Fe3+ and Mn2+ have been studied in a range of plagioclase feldspars, of intermediate composition. Many of these crystals have previously been investigated by TEM methods (McLaren and Marshall, 1974). The broad, central 27Al signals observed in labradorites have been interpreted in terms of an overall order/disorder of the Al/Si distribution. Spin Hamiltonian parameters have been determined for the Fe3+ spectra observed in labradorites and bytownites; these spectra were similar and yielded evidence of disordering of the Al/Si distribution. The severe limitations imposed by the variety of sites, the complex microstructures and the disordering, limit the structural information available from the resonance methods.

Effect of different cations on the properties of Sr0.5Ba0.5Nb2O6 ceramics

The effect of different cations and annealing process on pyroelectric and ferroelectric properties have been studied on Sr0.5 Ba0.5 Nb2O6 ceramics with Fe2O3, MnO2, Cr2O3 and La2O3 as additives. Improvement of those properties by doping and annealing have been found, and stabilization effects could explain some of the results. A very large zero field splitting may be derived from the EPR spectrum of Fe3+, which should indicate the existence of a very strong crystalline field and Fe3+ ions surrounded by oxygen vacancies as in PbTiO3 and SrTiO3.

Epr-experiments on Fe3+in KNbO3at room temperature

Abstract Epr-Spectra of Fe3+ in the orthorhombic phase of KNbO3 were observed with a helix-type spectrometer. The data for the substitutional centre are compared with those of BaTiO3.