Variation Of Hyperfine Parameters Research Articles

Atomic scale insights on the growth of BiFeO3 nanoparticles

This study provides new insights on the formation of the nanocrystallites of phase pure BiFeO3 prepared using sol–gel method with tartaric acid as the fuel as comprehended based on the local structure and magnetic hyperfine fields at Fe sites using Mossbauer spectroscopy. Important steps involved in the growth of the nanocrystallites of BiFeO3 in the sol–gel reaction are elucidated in a detailed manner in this study for the first time. Three important stages with the second stage marked by the formation of as high as 75% of nanocrystallites of BiFeO3 occurring over a narrow calcination temperature interval 700–723 K have been deduced in this study. Variation of hyperfine parameters with calcination temperature of the dried precursor gel leading to an increase in the mean size of crystallites of BiFeO3 has been deduced. The nanoparticles of BiFeO3 are deduced to exhibit weak ferromagnetic property in addition to being strongly ferroelectric based on the magnetization and P-E loop studies. Consequently an appreciable magneto electric coupling effect in terms of significant changes in P-E loop variation with the application of external magnetic field is elucidated in this study, which is comprehended based on the defects associated with BiFeO3 nanoparticles.

Mössbauer investigation of Co-doped Bismuth Ferrite prepared by the solution method

In this work, [Formula: see text] ([Formula: see text] = 0, 0.08) nanoparticles were synthesized by the solution method and their structural differences were studied. X-ray diffraction results show that the rhombohedral R3c space group and perovskite structures are detected in both samples, accompanied by an impurity phase. The (104) and (110) peaks merge when cobalt ions are doped. The decrease in lattice parameters indicates that the microstructure of the nanoparticles becomes gradually distorted. Mössbauer spectroscopy analysis at room temperature reveals an additional doublet due to the oxygen vacancies in [Formula: see text]. Hyperfine interactions, spatial spin-modulated structures and oxygen deficiencies around iron ions are also reflected in the observed spectra and variations in hyperfine parameters.

Iron spin state in silicate perovskite at conditions of the Earth's deep interior

We present a review of our recent work concerning the spin state of Fe2+ and Fe3+ in iron magnesium aluminium silicate perovskite, the most abundant phase in the Earth's interior. Experimental results obtained using Mössbauer spectroscopy (with a radioactive source and a Synchrotron Mössbauer Source) and nuclear forward scattering for a range of different sample compositions in both externally heated and laser-heated diamond anvil cells show clear trends in the variation of hyperfine parameters with pressure and temperature. These trends combined with reported total spin state measurements using X-ray emission spectroscopy on samples of similar composition support the conclusion that Fe2+ undergoes a high-spin to intermediate-spin transition near the top of the lower mantle and an intermediate-spin to low-spin transition near the bottom of the lower mantle. No spin transition is observed to occur in Fe3+ for samples with compositions relevant for the lower mantle.

Spin-Transfer Pathways in Paramagnetic Lithium Transition-Metal Phosphates from Combined Broadband Isotropic Solid-State MAS NMR Spectroscopy and DFT Calculations

Substituted lithium transition-metal (TM) phosphate LiFe(x)Mn(1-x)PO(4) materials with olivine-type structures are among the most promising next generation lithium ion battery cathodes. However, a complete atomic-level description of the structure of such phases is not yet available. Here, a combined experimental and theoretical approach to the detailed assignment of the (31)P NMR spectra of the LiFe(x)Mn(1-x)PO(4) (x = 0, 0.25, 0.5, 0.75, 1) pure and mixed TM phosphates is developed and applied. Key to the present work is the development of a new NMR experiment enabling the characterization of complex paramagnetic materials via the complete separation of the individual isotropic chemical shifts, along with solid-state hybrid DFT calculations providing the separate hyperfine contributions of all distinct Mn-O-P and Fe-O-P bond pathways. The NMR experiment, referred to as aMAT, makes use of short high-powered adiabatic pulses (SHAPs), which can achieve 100% inversion over a range of isotropic shifts on the order of 1 MHz and with anisotropies greater than 100 kHz. In addition to complete spectral assignments of the mixed phases, the present study provides a detailed insight into the differences in electronic structure driving the variations in hyperfine parameters across the range of materials. A simple model delimiting the effects of distortions due to Mn/Fe substitution is also proposed and applied. The combined approach has clear future applications to TM-bearing battery cathode phases in particular and for the understanding of complex paramagnetic phases in general.

Study of Fe-doped ZnO by Mechanical Alloying

Zn100−xOFex samples were obtained by mechanical alloying (MA) with different milling times. The purpose of this work was to analyze the variation of hyperfine parameters of the system with milling time. X-ray patterns show that pure ZnO under mechanical milling is not contaminated; additionally the system obtained by mechanical alloying has a wurtzite structure similar to pure ZnO. Mossbauer spectra show that all samples present two phases: paramagnetic and ferromagnetic. The milling time contributes to increase the paramagnetic phase; however, the Mossbauer spectra taken for samples milled during 36 and 99 hours indicates that there is a solubility limit for Fe atoms in ZnO lattice due that the spectra area remains nearly constant after 36 h. Mossbauer spectrometry shows that the Fe atoms which penetrate inside the ZnO matrix behave like Fe3+ and Fe2+.

Biomedical application of Mössbauer spectroscopy with a high velocity resolution: Revealing of small variations

Application of Mössbauer spectroscopy with a high velocity resolution for study different hemoglobins, ferritin, its models and chicken liver and spleen as well as normal and lymphoid chicken spleen demonstrated revealing of small variations of hyperfine parameters related to small variations of iron stereochemistry in biomolecules. These data demonstrate that Mössbauer spectroscopy with a high velocity resolution may be useful in biomedical research to distinguish small variations of iron-containing proteins in normal and pathological cases.

Mössbauer spectroscopy with high velocity resolution in the study of ordinary chondrites

Mossbauer spectroscopy with high velocity resolution was used to study of 11 ordinary chondrites from L and H chemical groups. Mossbauer spectra were recorded in 4,096 channels and then presented in 1,024 channels. An increase of velocity resolution allowed us to carry out more detailed analysis of ordinary chondrites and to decrease experimental error for evaluation of hyperfine parameters in comparison with previous chondrite Mossbauer spectra measured in 512 channels or less. Variations of hyperfine parameters were observed for corresponding iron bearing phases in chondrites. Two crystallographically non-equivalent octahedral sites M1 and M2 in olivine and pyroxene were revealed in Mossbauer spectra of bulk chondrite samples.

Co substitution effect on magnetic properties of magnetostrictive compounds Tb 0.36Dy 0.64(Fe 1−xCo x) 2 (0⩽ x⩽0.30)

The substitution effect of Co for Fe on magnetic properties of giant magnetostrictive compounds Tb 0.36Dy 0.64(Fe 1− x Co x ) 2 (0⩽ x⩽0.30) was examined by 57Fe Mössbauer measurements. It was found that the Co substitution did not change the easy magnetization direction (EMD). The average hyperfine fields and the deduced Fe moment increased with increasing Co content. The composition dependences of the magnetic transition temperatures, magnetization and magnetostrictions were consistent with the variation of hyperfine parameters, which can be ascribed to the 3d electrons transfer between Fe and Co atoms.

57Fe Mössbauer studies on MgAl xCr xFe 2-2 xO 4 spinel system

Based on 57Fe Mössbauer spectroscopy studies conducted at 300 K, the magnetic behaviour of the spinel ferrite system MgAl x Cr x Fe 2-2 x O 4 ( x=0.0–0.5) has been investigated. The Mössbauer spectra for x=0.0–0.2 exhibit two Zeeman sextets, one due to the Fe 3+ octahedral ions and the other due to the Fe 3+ tetrahedral ions, while the compositions x=0.3, 0.4 and 0.5 showed central paramagnetic doublet superimposed on the magnetic sextets. The variation of hyperfine parameters and origin of the central doublet on the magnetic sextets have been discussed.

A study of interfaces in the microcrystalline alloy Fe3Si by Mössbauer spectroscopy

The microstructure and hyperfine parameters of Fe3Si powder particles milled in a ball mill are investigated. A model of islands of original structure separated by veins of damaged structure (interfaces) is applied. The contents of both phases derived from Mossbauer spectra are changed by heal treatment. Variations of hyperfine parameters with phase composition are explained as the effect of fluctuations of the magnetization. The isomer shift shows a compression of iron atoms in the interfaces and lattice expansion in the islands of original structure. The enhancement of the hyperfine field in interfaces is explained by the appearance of large “surface-like” magnetic moments.

Mössbauer study of amorphous Fe-Er-B-Si ribbons

Melt-spun ribbons of amorphous Fe 80Er xB 20−x (0<×<4) and Fe 72Er 8B 12Si 8 metallic glasses have been studied by Mössbauer spectrometry in the temperature range 4K – 600K. The variation of hyperfine parameters with temperature and Erbium concentration is reported. Under applied magnetic field, samples exhibit a collinear ferromagnetic structure.

Electron spin resonance spectra of niobium(IV) complexes—III: Niobium(IV) chloride adducts with various pyridines

Niobium tetrachloride reacts with pyridine and various substituted pyridines to form complexes of the type NbCl 4 · 2L which have a trans geometry in solution. ESR spectra of these complexes show variations in hyperfine parameters which can be related to the inductive or resonance effect of the substituent. The antibonding ground state 1 B 2 > ∗ molecular orbital is quiete covalent for all of the complexes investigated.