Synthesis,structural, optical,and magnetic properties of Co doped,Sm doped and Co+Sm co-doped ZnS nanoparticles

The compositional, structural, optical and magnetic properties of ZnS, Zn_0.98Co_0.02S, Zn_0.98Sm_0.02S and Zn_0.96Co_0.02Sm_0.02S nanoparticles synthesized by a hydrothermal method are presented and discussed. X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) studies revealed that all the samples exhibited cubic structure without any impurity phases. X-ray photoelectron spectroscopy (XPS) results revealed that the Co and Sm ions existed in +2 and +3 states in these samples. The photoluminescence (PL) spectra of all the samples exhibited a broad emission in the visible region. The room temperature magnetization versus applied magnetic field (M–H) curves demonstrated that the Sm+Co doped nanoparticles exhibited enhanced ferromagnetic behavior compare to Co and Sm individually doped ZnS nanoparticles, which is probably due to the exchange interaction between conductive electrons with local spin polarized electrons on the Co²⁺ or Sm³⁺ ions. This study intensifies the understanding of the novel performances of co-doped ZnS nanoparticles and also provides possibilities to fabricate future spintronic devices.     

Temperature and concentration quenching of mid-IR photoluminescence in iron doped ZnSe and ZnS laser crystals

Concentration dependences of the mid-IR kinetic of luminescence at ⁵E?⁵T₂ transition in Fe:ZnSe and Fe:ZnS laser samples were studied in 14–300 K temperature ranges. Radiation lifetime in Fe:ZnSe samples measured using low doped samples with iron concentration 0.1×10¹⁸ cm^?3 was estimated to be 57 μs. The magnetic susceptibility for higher doped (C_Fe=38 and 112×10¹⁸ cm^?3) Fe:ZnSe samples was found to consist of a paramagnetic Curie–Weiss behavior arising from the weakly interacting Fe²⁺ ions and a diamagnetic ZnSe contribution plus a temperature-independent, field-dependent contribution possibly arising from very small amounts of aggregated Fe.     

Relationship between structural and magnetic properties in (Ti,Fe)O2 powders obtained by mechanical milling

Fe-doped TiO₂ samples with different Fe content were prepared by mechanical alloying starting from TiO₂ rutile and FeO. The samples were structurally and magnetically characterized by XRD, Mössbauer spectroscopy, X-ray absorption spectroscopy (XAS), AC-susceptibility and magnetization measurements. XAS results showed that Fe ions were incorporated into the rutile phase with oxygen coordination that was lower than that expected in this phase. The oxygen coordination number decreased with the increase of Fe²⁺ ions such as it was previously found in the milled samples of TiO₂ doped with hematite. The RT Mössbauer spectra were reproduced using two paramagnetic interactions, one corresponding to Fe²⁺ (δ∼0.87 mm/s) and the other to Fe³⁺ (δ∼0.31 mm/s). Magnetometry measurements showed the presence of paramagnetic and ferromagnetic-like interactions at room temperature. Although saturation and coercivity of the ferromagnetic phase increased with iron, the effective magnetic moment per iron atom decreased, probably due to the precipitation of Fe rich antiferromagnetic structures.     

Defect induced paramagnetism in lightly doped ZnS:Fe nanoparticles

Nanoparticles of ZnS:Fe (0, 1, 3, and 5 at%) were synthesized by a refluxing route at 80 °C. All the samples exhibited cubic structure as revealed by X-ray powder diffraction studies. Blue emission of undoped samples was totally quenched by Fe doping. Magnetic measurements showed that the undoped ZnS was diamagnetic whereas all the doped samples were paramagnetic at room temperature. EPR signal characteristic of Fe³⁺ was observed in all the doped samples at room temperature. The paramagnetism of the present samples is attributed to the presence of uncoupled Fe³⁺ ions mediated by cation vacancies.     

Graphite nanosheets doped with Fe, Ni, and N, synthesized in one step, and their unique magnetic performance

Graphite nanosheets (GNs) doped with N, Fe, or Ni were synthesized by pyrolysis of metal tetrapyridinoporphyrazine (MPTpz, M=Fe²⁺, and Ni²⁺) and a mixture of MPTpzs in a chemical vapor deposition furnace. The products obtained were characterized by scanning and transmission electron microscopy, and X-ray photoelectron spectroscopy. The magnetic properties of the GNs obtained were investigated at room temperature using a vibrating sample magnetometer with an applied field of −10 000-10 000 Gs. The results show the GNs obtained are terrace-like and ultra-thin, with very high aspect ratio. Fe, Ni and N atoms have been doped to the GNs successfully. There are two types of N atom that are introduced into pure carbon systems: pyrinidic and graphitic N atoms. The GNs obtained exhibit ferromagnetic behavior at room temperature. Sample S1, obtained by pyrolysis of a mixture of MPTpzs (M=Fe²⁺ and Ni²⁺), have the highest coercivity force. The saturation magnetization (M_s), remanent magnetization (M_r), and coercivity (H_c) values of sample S1 are 24.51 emu g⁻¹, 3.95 emu g⁻¹, and 207.34 Gs, respectively.     

Effects of doping site and pre-sintering time on microstructure and magnetic properties of Fe-doped BaTiO3 ceramics

The A-site substituted BaTiO₃ ceramics were prepared by solid-state reaction via partial substitution of Fe for Ba²⁺. By comparison with the B-site substituted sample made under similar conditions, the effect of Fe doping site on microstructure and magnetism was investigated using X-ray diffraction, Mössbauer spectroscopy and vibrating sample magnetometer. It is found that A-site substitution can be realized to a certain extent at 7 at% Fe addition, whereas impurities are observed at higher Fe concentrations. In the nominal (Ba_0.93Fe_0.07)TiO₃ sample, the Fe ions are present as Fe²⁺ and Fe³⁺, respectively, replacing A-site Ba²⁺ and octahedral B-site Ti⁴⁺ in hexagonal perovskite lattice. The double-exchange Fe²⁺-O²⁻-Fe³⁺ interactions produce ferromagnetism well above room temperature, but the saturation magnetization and the Curie temperature are both obviously lower than those for B-site substitution due to different magnetic exchange mechanisms. In the B-site substituted sample Ba(Ti_0.93Fe_0.07)O₃, the super-exchange interactions between Fe³⁺ on pentahedral and octahedral Ti⁴⁺ sites are responsible for ferromagnetism. These results mean that B-site substitution is a better way for Fe-doped BaTiO₃ system to obtain high-Curie-temperature ferromagnetism. Moreover, increasing pre-sintering time can further improve the magnetism of B-site substituted samples, through which the saturation magnetization for Ba(Ti_0.93Fe_0.07)O₃ is enhanced ∼6 times.     

Influence of rare-earth ions on the structure and magnetic properties of barium W-type hexaferrite

Barium W-type hexaferrite with composition Ba_0.95R_0.05Mg_0.5Zn_0.5CoFe₁₆O₂₇ where R=Y, Er, Ho, Sm, Nd, Gd, and Ce ions has been prepared by the double-sintering ceramic technique. Structure of the prepared samples has been characterized by the X-ray diffraction (XRD) technique. The XRD patterns at room temperature show the presence of secondary phase with the intensity of the secondary phase increasing with increasing ionic radius of the rare earth (RE) ions. The variation of the magnetic susceptibility (χ_M) with temperature in the range 300–750 K at different magnetic field intensities (1280, 1733 and 2160 Oe) was studied by using Faraday's method. The results show that the Curie temperature (T_C) increases regularly with increasing RE ionic radius then decreases again, after which it reaches maximum value at Sm ion of radius ≈1.04 Å. This behavior was explained on the basis of the changes in Fe³⁺–O–Fe³⁺ superexchange interaction. The effective magnetic moment μ_eff. of the investigated samples was discussed in view of varying the RE element as well as the magnetization of different sublattices.     

Micro Raman,Mossbauer and magnetic studies of manganese substituted zinc ferrite nanoparticles: Role of Mn

A series of Mn–Zn Ferrite nanoparticles (<15 nm) with formula Mn_xZn_1−xFe₂O₄ (where x=0.00, 0.35, 0.50, 0.65) were successfully prepared by citrate-gel method at low temperature (400 °C). X-ray diffraction analysis confirmed the formation of single cubic spinel phase in these nanoparticles. The FESEM and TEM micrographs revealed the nanoparticles to be nearly spherical in shape and of fairly uniform size. The fractions of Mn²⁺, Zn²⁺ and Fe³⁺ cations occupying tetrahedral sites along with Fe occupying octahedral sites within the unit cell of different ferrite samples are estimated by room temperature micro-Raman spectroscopy. Low temperature Mossbauer measurement on Mn_0.5Zn_0.5Fe₂O₄ has reconfirmed the mixed spinel phase of these nanoparticles. Room temperature magnetization studies (PPMS) of Mn substituted samples showed superparamagnetic behavior. Manganese substitution for Zn in the ferrite caused the magnetization to increase from 04 to18 emu/g and Lande's g factor (estimated from ferromagnetic resonance measurement) from 2.02 to 2.12 when x was increased up to 0.50. The FMR has shown that higher Mn cationic substitution leads to increase in dipolar interaction and decrease in super exchange interaction. Thermomagnetic (M–T) and magnetization (M–H) measurements have shown that the increase in Mn concentration (up to x=0.50) enhances the spin ordering temperature up to 150 K (blocking temperature). Magnetocrystalline anisotropy in the nanoparticles was established by Mossbauer, ferromagnetic resonance and thermomagnetic measurements. The optimized substitution of manganese for zinc improves the magnetic properties and makes these nanoparticles a potential candidate for their applications in microwave region and biomedical field.     

X-Ray photoelectron and mössbauer spectroscopy studies on molybdenum-bearing ferrite

The X-ray photoelectron spectra of Mo 3d electrons (232.4–232.9 and 229.4–229.6 eV) for Mo-bearing ferrites have suggested that molybdenum ions are in the 4+ valence state on the lattice points in the spinel structure. The XPS data for Mo 3d and Fe 2p electrons combined with the Mössbauer data at room temperature suggest that Fe₂MoO₄ takes a valence state (Fe²⁺)_tet[Fe²⁺Mo⁴⁺]_octO₄.     

The relationship between magnetic behaviour and local structure around Fe ions in Fe-doped TiO2 rutile

The magnetic and structural characterization of Ti_1−xFe_xO₂ (x=0.025, 0.05, 0.07, 0.125, and 0.15) samples prepared by mechano-synthesis using TiO₂ and Fe₂O₃ as starting materials are reported. XANES measurements performed at the Fe K-edge show that Fe ions are in 3+ oxidation state in the 7 at% Fe-doped sample and in a mixture of 2+ and 3+ oxidation states in the other samples. EXAFS results show the incorporation of Fe ions substituting Ti ones in the rutile TiO₂ structure. They also reveal a strong correlation between the number of oxygen nearest neighbours and the Fe²⁺ fraction, i.e the number of oxygen near neighbours decreases when the Fe²⁺ fraction increases. All samples present ferromagnetic-like behaviour at room temperature. We found a clear dependence between saturation magnetization and coercivity with the fraction of Fe²⁺ and/or the number of Fe near neighbour oxygen vacancies.     

Structural, calorimetric and magnetic properties study of the Cu0,91Fe0,09O system

In this work the Cu_0.91Fe_0.09O nanocrystalline system was prepared via the co-precipitation method. Using Mössbauer Spectrometry, X-Ray Diffraction, Vibrating Sample Magnetometry, Thermogravimetry and Differential Scanning Calorimetry, we study the magnetic behavior, and the structural and calorimetric properties of this system. X-ray diffraction shows only the presence of the CuO structural monoclinic phase, suggesting that Cu atoms are substituted by Fe ones. This hypothesis was confirmed by Mössbauer spectrometry at room temperature, because it shows that the spectrum is formed by two doublets, which correspond to Fe^?+?2 and Fe^?+?3 sites. Hysteresis cycles obtained by vibrating sample magnetometry detect a soft ferromagnetic behavior at room temperature with coercive fields between 8 and 20 Oe. At T = 20 K the sample shows a hard-magnetic behavior. The thermogravimetry results show a Néel temperature (T _N > 440 °C). The differential scanning calorimetry curve show two endothermic peaks in the 90–120 °C range.     

A Mössbauer effect investigation of the magnetic behaviour of (Fe,Co)S1 + x solid solutions

The Mössbauer spectra of (Fe, Co)S_{1 + x} were recorded at room temperature and 4.2 K for samples of varying composition to study the magnetic behaviour of the solid solutions. The Mössbauer spectra are split magnetically at iron concentrations above 16% Fe. For samples with less than 16%Fe, the Mössbauer spectra show no evidence of magnetic splitting down to 4.2 K. The room temperature centre shift data appear to vary continuously with composition and the hyperfine magnetic field decreases with decreasing Fe²⁺ concentration. A Mössbauer spectrum of ⁵⁷Fe:CoS at 4.2 K in an external field of 25 kOe showed no evidence of magnetic splitting beyond that caused by the applied field, indicating a net zero internal field.A high spin to low spin transition in Fe²⁺ is ruled out as being responsible for the observed magnetic behaviour on the basis of the centre shift data. The Mössbauer data are interpreted to indicate a substantial increase in electron delocalization towards the ligands as the 〈M-S〉 distance decreases with decreasing Fe²⁺concentration. This causes a reduction in the magnitude of the internal magnetic field contributions as well as a decrease of shielding of the nucleus, giving rise to the observed Mössbauer parameters.The Mössbauer spectrum of ⁵⁷Fe:CoS at room temperature is compared with the spectrum of FeS above the 6.7 GPa phase transition at room temperature. The similarities of the centre shift and the 〈M-S〉 distance in the two phases indicate that covalency may also be responsible for the observed high pressure behaviour of FeS, and not the presence of Fe³⁺ as was originally suggested.     

Effect of impurity concentration on optical and magnetic properties in ZnS:Cu nanoparticles

To obtain enhanced room temperature ferromagnetism (RTFM) along with the increase in optical bandgap in the compound semiconductors has been an interesting topic. Here, we report RTFM along with increase in energy bandgap in chemically synthesized Zn_1−xCu_xS (0 ≤ x ≤ 0.04) DMS nanoparticles. Structural properties of the synthesized samples studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show the formation of cubic phase Cu doped ZnS nanoparticles of ~3–5 nm size. An intrinsic weak ferromagnetic behavior was observed in pure ZnS sample (at 300 K) which got increased in Cu doped samples and was understood due to defect induced ferromagnetism. UV–vis measurement showed increase in the energy bandgap with the increase in Cu doping. The PL study suggested the presence of sulfur and zinc vacancies and surface defects which were understood contributing to the intrinsic FM behavior.     

Polaronic and charge ordering effects in Pr 0.5 Sr 0.5 Mn 1− x Fe x O 3

In this work we report the results of X-ray diffraction and Mössbauer spectroscopy for the systems Pr_0.5Sr_0.5Mn_1???x Fe _x O₃ (with x?=?0.05, 0.10, 0.15, 0.20, 0.25, 0.30). XRD patterns indicated that all samples were single phase with slightly distorted orthorhombic symmetry. Room temperature Mössbauer spectra are all quadrupole split, indicating paramagnetic relaxation of the Fe moment for all values of Fe concentrations. The spectra are fitted with two doublet components associated with Fe^3?+? ions in octahedral sites with different distortions. Mössbauer spectra recorded at liquid nitrogen temperature for this system also indicate paramagnetic relaxation of the Fe moments down to liquid nitrogen temperature (LNT). In these spectra a third quadrupole component with quadrupole splitting close to zero develops. This component is associated with the delocalization of the charge carriers and the consequent disappearance of lattice distortions produced by the polaronic effect at room temperature. The component with the high quadrupole splitting (0.81 to 1.07 mm/s) results from Jahn–Teller distortion as a consequence of charge ordering transition at low temperature.     

Optical and ESR studies on Fe doped ZnS nanocrystals

Zn_1 − xFe_xS (x=0.0, 0.1, 0.2, 0.4 and 0.6) nanocrystals have been obtained by chemical co-precipitation from homogeneous solutions of zinc and iron salt compounds, with S²⁻ as precipitating anion formed by decomposition of thiophenol. The TEM micrographs show a spherical shape for ZnS nanocrystals and their average size is around 7 nm. The optical absorption spectra indicate a blue shift of the absorption edge with increasing Fe-content. The luminescence of nanoparticles excite at about 370 nm with an emission peak at around 490 nm. At room temperature, ESR signal characteristic of Fe³⁺ was observed in samples of all concentrations.     

Structural and magnetic investigations of sub-nano Mn-Mg ferrite prepared by wet method

Manganese-magnesium ferrite nanoparticles Mn_1−xMg_xFe₂O₄; 0≤x≤0.25 were prepared by the co-precipitation route. The samples were characterized by X-ray diffraction (XRD), which confirms the single phase spinel structure. Crystallite size, calculated from the (3 1 1) peak using the Scherrer formula, was found to increase with increasing Mg²⁺ concentrations and was found to be within the range 3-6 nm. TEM was also used to characterize the microstructure of nanosized Mn_1−xMg_xFe₂O₄. Nominal composition of the samples was determined by Atomic Absorption analysis (AA). Hysteresis loops of manganese-magnesium ferrite were obtained at room temperature and revealed lower saturation magnetization values associated with nanocrystalline Mn_1−xMg_xFe₂O₄ particles. This behavior was attributed to structural distortion of surface spins compared to that of the bulk one.     

Studies on Structural, Magnetic and Thermal Properties of xFe2TiO4-(1−x)Fe3O4 (0≤x≤1) Pseudo-binary System

The xFe₂TiO₄-(1−x)Fe₃O₄ pseudo-binary systems (0≤x≤1) of ulvöspinel component were synthesized by solid-state reaction between ulvöspinel Fe₂TiO₄ precursors and commercial Fe₃O₄ powders in stochiometric proportions. Crystalline structures were determined by X-ray powder diffraction (XRD) and it was found that the as-obtained titanomagnetites maintain an inverse spinel structure. The lattice parameter a of synthesized titanomagnetite increases linearly with the increase in the ulvöspinel component. ⁵⁷Fe room temperature Mössbauer spectra were employed to evaluate the magnetic properties and cation distribution. The hyperfine magnetic field is observed to decrease with increasing Fe₂TiO₄ component. The fraction of Fe²⁺ in both tetrahedral and octahedral sites increases with the increase in Ti⁴⁺ content, due to the substitution and reduction of Fe³⁺ by Ti⁴⁺ that maintains the charge balance in the spinel structure. For x in the range of 0 ≤x≤0.4, the solid solution is ferrimagnetic at room temperature. However, it shows weak ferrimagnetic and paramagnetic behavior for x in the range of 0.4<x≤0.7. When x>0.70, it only shows paramagnetic behavior, with the appearance of quadrupole doublets in the Mössbauer spectra. Simultaneous differential scanning calorimetry and thermogravimetric analysis (DSC-TGA) studies showed that magnetite is not stable, and thermal decomposition of magnetite occurs with weight losses accompanying with exothermic processes under heat treatment in inert atmosphere.     

Curie temperature,crystallization temperature and electrical resistivity as a function of composition for Fe80-xMoxB20 metallic glasses

The influence of the substitution of small amounts of Fe with Mo (0–10 at.%) in a Fe₈₀B₂₀ metallic glass on the Curie temperature, crystallization temperature and room temperature electrical resistivity is reported. A decrease in Curie temperature of approximately 40 K/at.% Mo is observed. The crystallization temperatures show a small increase with increasing Mo-content, and the room temperature electrical resistivity of the as quenched samples is essentially independent of the Mo-content (?^am(295 K) ～ 128 μχ-cm).     

ZnO-Fe3O4 composite prepared by sol-gel method with H2 deoxidation

Fe doped ZnO powder samples (Fe/Zn=0.05 and 0.1) were prepared by sol-gel method with H₂ deoxidation at 450 ^°C for several hours or just heated in air at the same temperature. It was showed by vibrating sample magnetometer (VSM) that samples heat treated in H₂ could show strong ferromagnetism at room temperature while samples treated in air only show very weak magnetism. XRD using Co kα X-ray revealed that the samples heated in H₂ were not pure phase but like a granular system and the magnetism mainly results from Fe₃O₄ in samples while samples heated in air showed pure ZnO phase. Our work indicated that H₂ deoxidation treatment may be an effective technique to fabricate such magnetic semiconductor-like materials with Curie temperature higher than room temperature.     

Photoluminescence and magnetic properties of Fe-doped ZnS nano-particles synthesized by chemical co-precipitation

This paper is focusing on the synthesis of Zn_1−xFe_xS nano-particles with x = 0, 0.1 and 0.2 by chemical co-precipitation method, the prepared of which are characterized by XRD, EDS, TEM, PL, magnetization versus field behavior and M-T curve. In the XRD patterns, Zn_1−xFe_xS nano-particles are shown of cubic zinc blende structure, and the broadening diffraction peaks consistent with the small-size characteristic of nano-materials. The diameter of nano-particles is between 3.3 and 5.5 nm according to the HR-TEM images. The EDS data confirm the existence of Fe ions in Fe-doped ZnS nanoparticles. There we found that Fe-doping did not import new energy bands or defect states, but reduced the intensity of PL peaks. The magnetization versus field behaviors were illustrated by the M-H curves at both 5 K and 300 K, respectively, where no remanence or coercive force was observed. This phenomenon indicates that the Zn_1−xFe_xS (x = 0.1) nano-particles are superparamagnetic. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves further reveal that the blocking temperature (T_B) of the superparamagnetic behavior might be below 5 K.