Mossbauer Spectroscopy

Abstract Schiff base 4-[(2-hydroxy-3-methoxybenzylideneamino)-N-(5-methylisoxazol-3-yl)benzene-sulfonamide has been synthesized from the reaction of 4-amino-N-(5-methylisoxazol-3-yl)benzenesulfonamide(sulfamethoxazole) with 2-hydroxy-3-methoxybenzaldehyde. It has been characterized by elemental analysis, MS, IR, 1H NMR, 13C NMR, HETCOR and UV–Visible techniques. The structure of it also has been examined crystallographically. For the compound exist as dominant form of enol-imines in both the solid state and the solutions. It crystallizes in the monoclinic space group P21/c with a = 8.2694(7), b = 8.3453(5), c = 26.260(2) Å, β = 97.142(7) °, V = 1798.1(2) Å3, D x  = 1.431 g cm−3, R 1 = 0.0529 and wR 2 = 0.1370 [I > 2σ(I)], respectively. Index Abstract The tautomerism in the Schiff base ligands plays an important role for distinguishing their photochromic and thermochromic characteristics. Both phenomena is associated with a proton transfer (enol-imine, O–H···N, keto-amine, O···H–N).

A systematic study has been made of the initial corrosion products which form on mild steel capons exposed near the coastal region of Oman and at some industrial areas. The phases and compositions of the products formed at different periods of exposure were examined by using Mössbauer spectroscopy (295 and 78 K) and X-ray diffraction (XRD) techniques. The results show that lepidocorcite and maghemite are early corrosion products and goethite starts to form after 2 months of metal exposure to the atmosphere. Akaganeite is an early corrosion product but it forms in marine environments only, which reflects the role of chlorine effect in the atmosphere. The 12 months coupons showed the presence of goethite, lepidocorcite and maghemite, but no akaganeite being seen in the products of one of the studied areas.

, Synthesis of nanocrystalline spinel ferrite (MFe 2 O 4 , M = Zn and Mg) by solution combustion method: Influence of fuel to oxidizer ratio, Abstract: Fuel to oxidizer ratio is a critical parameter that determines the properties of nanocrystalline ferrites prepared by solution combustion method. In this study, the influence of fuel to oxidizer ratio on the purity of phase and physical properties of Zinc and Magnesium ferrite nanoparticles prepared by solution combustion method using glycine as fuel is reported. PXRD and FTIR studies on the samples prepared under fuel lean and fuel rich conditions show that there is a gradual variation in the impurity phase as the F/O ratio is varied. Magnetic studies using VSM and Mössbauer spectroscopy show that a reducing environment is created during the combustion process, which influences the magnetic properties of the samples. Mössbauer studies also show that cation redistribution between the tetrahedral and octahedral sites of the as prepared samples also is an important factor which determines the magnetic properties.

Hyperfine interaction techniques like Mossbauer spectroscopy are very sensitive tools to study the local probe interactions in dilute magnetic semiconductors. We report here a Mossbauer study on the concentration dependence in Fe0.008Ge1 − x Tex for x = 0, 0.008, 0.016, 0.03 and 0.05. At room temperature magnetic interactions were observed for all concentrations of Te and the population of magnetic site was found to increase gradually with the Te concentration. A constant magnetic hyperfine field of 136 KOe was found. A quadrupole doublet due to the FeTe2 compound phase was also seen.

The structural and magnetic properties of lithium ferrite nanoparticles synthesized through the solution combustion route at different fuel to oxidizer ratio are studied using different techniques. Powder X-ray diffraction studies show that the fuel to oxidizer ratio is a critical parameter that determines the phase purity and degree of order of the samples. Magnetic studies show that the saturation magnetization and coercivity are comparable to those reported for lithium ferrites prepared using other methods. Saturation magnetization of Li0.8 sample at room temperature is 60 emu/g and is close to the bulk value. The hyper-fine parameters obtained from the Mössbauer spectra of Li0.6 and Li0.8 also match the reported values of phase pure samples. Mössbauer spectra of samples prepared at stoichiometric and fuel rich conditions show the presence of Fe 2+ cations in the ferrite phase, indicating that a reducing environment which reduces Fe 3+ to Fe 2+ ions is created as the fuel to oxidizer ratio is increased. The variation in the structural and magnetic properties of the samples, combined with TGA and FTIR studies, shows that the fuel lean condition is more appropriate for the direct formation of single phase lithium ferrite nanoparticles.

In this article, we present the results of Mössbauer spectroscopy measurements on the alloys: (A) (Ho 0.3Y 2.7)Fe 5O 12, (B) (Ho 1.5Y 1.5)Fe 5O 12; and (C) Tb 3Fe 5O 12. The spectra are collected at 4.2 K and at room temperature (RT). Mössbauer spectra of samples A and B show the presence of two magnetic sextets corresponding to iron atoms in octahedral “a” and in tetrahedral “d” sites. The spectrum for sample C at RT shows two magnetic sextets with hyperfine fields significantly smaller than those for samples A and B. This reduction in hyperfine field is associated with fast magnetic relaxations in Tb-iron garnet (TIG) at room temperature. At liquid helium temperature, the spectrum of TIG shows three magnetic sextets. Two of these are associated with the canted spin structure at low temperature.

The properties of nanocrystalline Ni0.5Zn0.5Fe2O4 synthesized by an auto-combustion method have been investigated by magnetic measurements and Mössbauer spectroscopy. The as-synthesized single phase nanosized ferrite powder is annealed at different temperatures in the range 673–1,273 K to obtain nanoparticles of different sizes. The powders are characterized by powder X-ray diffraction, vibrating sample magnetometer, transmission electron microscopy and Mössbauer spectroscopy. The as-synthesized powder with average particle size of ~9 nm is superparamagnetic. Magnetic transition temperature increases up to 665 K for the nanosized powder as compared to the transition temperature of 548 K for the bulk ferrite. This has been confirmed as due to the abnormal cation distribution, as evidenced from room temperature Mössbauer spectroscopic studies.

Magnetic multiwalled carbon nanotube (MWCNTs) nanocomposites have been created by the assembly of Mg-Ni-Ti substituted barium ferrite nanoparticles onto surface of MWCNTs. X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to demonstrate the successful attachment of ferrite nanoparticles to MWCNTs. Vibrating sample magnetometer (VSM) confirms the relatively strong dependence of saturation of magnetization and coercivity with the volume percentage of MWCNTs. Reflection loss evaluations indicated that the nanocomposites display a great potential application as wide-band electromagnetic wave absorbers.

Iron-based layered double hydroxides (LDHs) have the general formula [MII(1-x)MIIIx(OH)2]x+·[(x/n) An−, m H2O]x− and contain a molar fraction of iron, i.e. FeII or FeIII situated in the cationic layers, higher than 50%. LDHs containing FeII species are interesting materials for several applications such as the reduction of anionic pollutants or the degradation of organic pollutants. They are mostly prepared either by coprecipitation of dissolved species or by oxidation of hydroxylated FeII species. The synthesis routes were visualised in binary and ternary mass-balance diagrams. The LDH[FeII–FeIII] particles were well crystallised hexagonal plates, the size of which diminishes rapidly when divalent or trivalent cations substitute ions. The LDH[FeII–FeIII–CO3] transformed into a mixture of magnetite Fe3O4 and siderite FeCO3 in alkaline conditions, but the adsorption of silicate or phosphate anions on the lateral faces of the crystal prevented this decomposition. In oxic conditions, t...

In this work we report a study of the magnetic behavior of ferrimagnetic oxide CoFe2O4 and ferrimagnetic oxide/ferromagnetic metal CoFe2O4/CoFe2 nanocomposites. The latter compound is a good system to study hard ferrimagnet/soft ferromagnet exchange coupling. Two steps were used to synthesize the bimagnetic CoFe2O4/CoFe2 nanocomposites: (i) first preparation of CoFe2O4 nanoparticles using the a simple hydrothermal method and (ii) second reduction reaction of cobalt ferrite nanoparticles using activated charcoal in inert atmosphere and high temperature. The phase structures, particle sizes, morphology, and magnetic properties of CoFe2O4 nanoparticles have been investigated by X-Ray diffraction (XRD), Mossbauer spectroscopy (MS), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) with applied field up to 3.0 kOe at room temperature and 50K. The mean diameter of CoFe2O4 particles is about 16 nm. Mossbauer spectra reveal two sites for Fe3+. One site is related to Fe in an octahedral coordination and the other one to the Fe3+ in a tetrahedral coordination, as expected for a spinel crystal structure of CoFe2O4. TEM measurements of nanocomposite show the formation of a thin shell of CoFe2 on the cobalt ferrite and indicate that the nanoparticles increase to about 100 nm. The magnetization of nanocomposite showed hysteresis loop that is characteristic of the exchange spring systems. A maximum energy product (BH)max of 1.22 MGOe was achieved at room temperature for CoFe2O4/CoFe2 nanocomposites, which is about 115% higher than the value obtained for CoFe2O4 precursor. The exchange-spring interaction and the enhancement of product (BH)max in nanocomposite CoFe2O4/CoFe2 have been discussed.

Spinel nickel ferrite with nominal composition NiFe2−xSbxO4 (where x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1) has been synthesized by the reverse microemulsion method. The samples synthesized were characterized by XRD, FTIR, TGA/DTGA, SEM, AFM, Mossbauer Spectroscopy and DC electrical resistivity measurements. The XRD analysis confirmed the formation of single spinel phase and the crystallite size was found to be in the range of 8–38 nm. The particle size of the synthesized samples was also confirmed by the AFM and SEM which was found in the range of 5–45 nm and 10–45 nm, respectively and this size is small enough for obtaining the suitable signal-to-noise ratio in high density recording media. The Mossbauer spectra of samples showed two well-resolved Zeeman patterns corresponding to A and B sites and also observed a doublet at higher substitution. The DC electrical resistivity showed an interesting behavior with temperature and observed a metal-to-semiconductor transition temperature (TM–S...