Effect of preparation procedure on the magnetic and transport properties of double perovskite Sr2FeMoO6

Ordered and disordered double perovskite Sr2FeMoO6 ceramics have been investigated by powder x-ray diffraction,magnetic and transport measurements, as well as Moessbauer spectroscopy. The heavily disordered sample can be acquired by annealing the ordered samples in argon. The annealing procedure affects not only the nature of grain boundaries but also the grain itself. The evidence of Moessbauer spectra performed at 77 and 300K indicates that there exist small oxygen deficient clusters of SrFeO3-y in the disordered sample. The paramagnetic Fe^4 and Fe^3 ions in the compound subsist down to 77K and the ratio of Fe^4 /Fe^3 increases with decreasing temperature.     

Experimental and theoretical XANES study of the effcets of Fe—Mg solid solution in the enstatit—ferrosilite series

Synthetic orthopyroxenes in the join enstatite-ferrosilite (Mg2Si2O6-Fe2Si2O6)have been studied by XANES with the aim to interpret the variations found in the spectra and evaluate the effects of the Mg-Fe substitution in the orthopyroxene(OPX) structure.The experimental Fe-and Mg-K edge XANES spectra show variations of the peaks intensity as a function of the chemical composition of the samples along the EN-FS join.In the region of the Fe edge,the intensity ratio between peak A and B(IB/IA)varies linearly(R=0.99) with the Mg/Fe substitution. Multiple scattering calculation have been performed both at the Fe and Mg K-edge,to study the geometrical modifications of the M1 and M2 octahedral sites induced by the Mg-Fe substitutions.The spectra,obtained locating Fe(or Mg)in both M1 and M2 and weighing the contributions using the occupancy data for the M1 and M2 sites determined by XRD,allow to discriminate the effects to the total spectrum due to Fe(Mg) located in each sites separately.     

Glass Formation Ability and Kinetics of the Gd55A120Ni25 Bulk Metallic Glass

We report a new bulk glass-forming alloy GdssA12oNi25. The bulk sample of the alloy is prepared in the shape of rods in diameter 2ram by suction casting. The rod exhibits typical amorphous characteristics in the x-ray diffraction pattern, paramagnetic property at 30OK, distinct glass transition and multi-step crystallization behaviour in differential scanning calorimetry traces. The gJass formation ability of the alloy is investigated by using the reduced glass transition temperature Trg and the parameter γ- Kinetics of glass transition and primary crystallization is also studied. The fragility parameter m obtained from the Vogel-Fulcher-Tammann dependence of glass transition temperature Tg on In φ （φ is the heating rate） classifies the bulk metallic glasses into the intermediate category according to Angell＇s classification.     

Moessbauer study and magnetic properties of electrochemical material LiFePO4

Magnetic properties and crystal symmetry of electrochemical material LiFePO4 have been investigated by Moessbauer spectroscopy and magnetization measurement. Magnetization reveals the antiferromagnetic nature of LiFePO4. Temperature dependence of inverse susceptibility and that of hyperfine field confirm that there is an antiferromagnetic-paraxaagnetic transition at about 50K.     

Radio-frequency Mössbauer spectra of the “easy”-plane type magnetic system (FeBO3)

The theory of formation of the RF Mössbauer spectra for the “easy”-plane type magnetics (FeBO₃) and for various types of RF field polarization is presented. Experiments using both linearly and circularly polarized external RF fields were carried out at different temperatures. At room temperature the experimental spectra for both cases are well described by switching hyperfine (hf) field model. At temperatures close to the Neel temperature (335 K), the spectra in the oscillating and rotating RF field were obtained and their forms are described by models of switching and rotating hf field, respectively.     

A temperature and magnetic field dependence Mössbauer study of ɛ-Fe2O3

?-Fe₂O₃ was synthesized as nanoparticles by a pre-vacuum heat treatment of yttrium iron garnet (Y₃Fe₅O₁₂) in a silica matrix at 300°C followed by sintering in air at 1,000°C for up to 10 h. It displays complex magnetic properties that are characterized by two transitions, one at 480 K from a paramagnet (P) to canted antiferromagnet (CAF1) and the second at ca. 120 K from the canted antiferromagnet (CAF1) to another canted antiferromagnet (CAF2). CAF2 has a smaller resultant magnetic moment (i.e. smaller canting angle) than CAF1. Analysis of the zero-field Mössbauer spectra at different temperatures shows an associated discontinuity of the hyperfine field around 120 K. In an applied field, the different magnetic sublattices were identified and the directions of their moments were assigned. The moments of the two sublattices are antiparallel and collinear at 160 K but are at right angle to each other at 4.2 K.     

Mössbauer study of iron oxide modified montmorillonite

Montmorillonite particles were modified by iron oxides using the precipitation process with the aim to monitor the differences in the structural and magnetic properties of intercalated and adsorbed Fe³⁺. The Mössbauer spectra recorded at 5 K in zero and 6 T external fields, IR spectra and TG curves measured in zero and 32 mT fields identified the ferrihydrite pillars in an interlayer space of the montmorillonite structure and γ-Fe₂O₃ nanoparticles adsorbed on the mineral surface. The temperature dependent Mössbauer spectra (25–300 K) reflect the superparamagnetic behaviour of maghemite nanoparticles and ferrihydrite pillars with the blocking temperatures of about 80 and 25 K, respectively.     

The Unusual Mössbauer Spectrum of Beryl

The Mössbauer spectra of several aquamarine samples have been obtained in the temperature range of 4.2–500 K. A common feature observed in all room-temperature spectra is the presence of an asymmetric Fe²⁺ doublet (ΔE _Q～2.7 mm/s, δ～1.1 mm/s), with a very broad low-velocity peak. This asymmetry is not caused by preferred orientation since the spectrum collected under the magic angle did not show any difference in the line intensities, nor is it caused by the superposition of a Fe³⁺ doublet. At 4.2 K the spectrum of a deep-blue beryl could be well fitted with three symmetrical doublets, with the major Fe²⁺ doublet accounting for 87% of the total spectral area. At 14 K the symmetry remains, but at 30 K the low-velocity peak is again broad. Surprisingly, the spectrum at 500 K also shows a broad, but symmetrical doublet, with a clear splitting of the lines indicating the presence of at least two Fe²⁺ components. The room-temperature spectrum obtained after the 500 K run shows the same features as before the heating. A meaningful fit for the room-temperature spectrum, as well as an explanation for the temperature dependence of the Mössbauer spectra, are discussed.     

Metallurgical behaviour of iron in brass studied using Mössbauer spectroscopy

The behaviour of small amounts of Fe in brass is investigated using Mössbauer spectroscopy. Different samples, made from the same ingot material, but run through different annealing temperatures and duration times and then quenched to room temperature, have different amount of γ-Fe. The present work shows that a suitable heat treatment can increase the amount of these precipitations and, that a heat treatment at 650°C is the optimal one for having the highest amount of this phase.     

Mössbauer study of some biological iron complexes

Some biological complexes containing iron are investigated experimentally at room temperature using the Mössbauer resonance. The complexes show quadrupole doublet and Kramer’s degeneracy is found to exist. The electric field gradient, difference ins-electron densities and quadrupole coupling constant have been calculated in each case. These parameters are used to obtain information on the surroundings of the Mössbauer atom     

A study by Mössbauer spectroscopy of iron-pollucite

Summary Synthetic samples of pollucite with different amounts of aluminum-iron substitution, or with both aluminum-boron and aluminum-iron substitutions, were investigated by M?ssbauer spectroscopy. Experimental data show that the tetrahedral sites of silicon and aluminum ions are substantially equivalent, but with iron substitutions as large as 75% or more, lattice deformations are originated which make the sites different.     

Mössbauer spectroscopy: Application in biomedical research

The results of the application of Mössbauer spectroscopy in biomedical research were briefly reviewed. The main directions of biomedical application and possibilities of Mössbauer spectroscopy to study the molecular nature of diseases were considered.     

Mössbauer studies of hyperfine fields in disordered Fe2CrAl

Heusler-like alloy Fe₂CrAl was prepared and studied. Structure determination was done by X-ray. The structure was found to conform to the B₂ type. Magnetic hyperfine fields in this sample were studied by the Mössbauer effect. The Mössbauer spectra were recorded over a range of temperature from 40 to 296 K. The Mössbauer spectra showed the co-existence of a paramagnetic part with a magnetic hyperfine portion at all recorded temperatures. Even with the distribution in the magnetic hyperfine field, the average hyperfine field follows the (T/T _c)^3/2 law. The paramagnetic part of the hyperfine field is explained in terms of the clustering of Cr atoms.