Structural, 57 Fe Mössbauer and XPS studies of mechanosynthesized nanocrystalline Nd0.33Eu0.67Fe1-xCrxO3 particles

We report on the structure and surface composition of Nd0.33Eu0.67Fe1-xCrxO3 (x = 0.0, 0.3, 0.5, 0.7, 0.9 and 1.0) nanoparticles (∼30 nm) mechanosynthesized at temperatures that are ∼ 470– 700 °C lower than those at which the pure and doped pristine materials conventionally form. XRD Rietveld and FT-IR analyses show that with increasing x the lattice parameters decrease and the bond lengths and angles vary in a way that reduces crystalline distortion. Whilst the majority of the Eu3+/Nd3+ and Fe3+/Cr3+ cations occupy the normal perovskite-related A- and B-sites, respectively, ∼ 5% of them exchange sites. 57Fe Mössbauer spectroscopy confirms the presence of these antisites and reveals a superparamagnetic behaviour at 298 K that enhances with increasing x. XPS measurement reveals a complex surface composition of the nanoparticles with traces of Eu2O3, Nd2O3, Cr2O3 and Fe2O3 as well as partial O2--deficiency

The hyperfine properties of a hydrogenated Fe/V superlattice

: We study the effect of hydrogen on the electronic, magnetic and hyperfine structures of an iron-vanadium superlattice consisting of three Fe monolayers and nine V monolayers. The contact charge density ({\rho}), the contact hyperfine field (Bhf) and the electronic field gradient (EFG) at the Fe sites for different H locations and H fillings are calculated using the first principle full-potential linear-augmented-plane-wave (FP-LAPW) method . It is found that sizeable changes in the hyperfine properties are obtained only when H is in the interface region.Comment: 6 pages, 2 figures, 3 tables, ICAME 2011 conference (Kobe, Japan

Magnetic properties of nanocrystalline Fecu(x)Cu(1-x) alloys prepared by ball milling

X-ray diffraction, Mossbauer and magnetization measurements were used to study FexCu1-x alloys prepared by ball-milling. The X-ray data show the formation of a nanocrystalline Fe-Cu solid solution. The samples with xgreater than or equal to0.8 and xless than or equal to0.5 exhibit bcc or fcc phase, respectively. Both the bcc and fcc phases are principally ferromagnetic for xgreater than or equal to0.2, but the sample with x=0.1 remains paramagnetic down to 78 K. The influence of the local environment on the hyperfine parameters and the local magnetic moment are discussed using calculations based on the discrete-variational method in the local density approximation

A complete study of amorphous iron phosphate structure

In-depth structural studies have been carried out on amorphous FePO 4 prepared by two different methods, and on amorphous LiFePO 4 prepared by electrochemical insertion of Li. The local environment of Fe in these samples was investigated using Mössbauer spectroscopy and X-ray absorption spectroscopy. X-ray and neutron diffraction and transmission electron microscopy have been applied to elucidate the first complete structural study of these materials. The Fe environment in amorphous FePO4 was found to be similar to that in quartz FePO4 where every Fe is surrounded by four oxygen atoms. However, the Fe environment in amorphous LiFePO4 is affected by the appearance of Fe metal in this sample as a consequence of Li insertion. Small angle scattering measurements confirmed the presence of nm-scale internal structure in the amorphous FePO4 prepared by thermal decomposition and in amorphous LiFePO4. © 2013 Elsevier B.V. All rights reserved

The Formation of Nanocrystalline SrFeO3−δ Using Mechano-Synthesis and Subsequent Sintering: Structural and Mössbauer Studies

The influence of mechanical milling and subsequent sintering of a 2:1 molar mixture of SrCO3 and α-Fe2O3 on the formation of SrFeO3−δ pervoskite-related nanocrystalline particles is investigated. The structural evolution during the formation process is systematically investigated using X-ray diffraction, thermal analysis, X-ray photoelectron spectroscopy and Mössbauer spectroscopy. Premilling the mixture in air for 120 h leads to the incorporation of Sr2+ in the α-Fe2O3 crystal structure thus facilitating the formation of a 2:1 nanocrystalline mixture of SrFeO3 and SrFeO2.875 by sintering the pre-milled mixture in air at 800 °C (12 h). This temperature is ∼300 °C lower than those at which SrFeO3−δ phases are synthesized by the conventional ceramic techniques. Pre-milling the precursors was found to result in a smaller oxygen deficiency (δ) relative to conventional ceramic synthesis of SrFeO3−δ. Rietveld refinement of the X-ray diffraction shows the interatomic distances in the resulting SrFeO2.875 nanocrystalline phase to be slightly different from those of the conventionally prepared bulk leading, in turn, to a crystal structure with tilted polyhedral cationic sites. This structural distortion is related to both small-size and surface effects in the nanoparticles that have no counterparts in the corresponding bulk material. The surface structure of the attained SrFeO3−δ nanocrystalline particles shows a significant partial reduction of Fe4+ to Fe3+ due to ambient conditions and the presence of an appreciable amount of SrCO3 as well

Investigating Exchange Bias and Coercivity in Fe₃O₄-gamma-Fe₂O₃ Core-Shell Nanoparticles of Fixed Core Diameter and Variable Shell Thicknesses

We have carried out extensive measurements on novel Fe3O4-gamma-Fe2O3 core-shell nanoparticles of nearly similar core diameter (8 nm) and of various shell thicknesses of 1 nm (sample S1), 3 nm (sample S2), and 5 nm (sample S3). The structure and morphology of the samples were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The direct current (DC) magnetic measurements were carried out using a superconducting quantum interference device (SQUID). Exchange bias and coercivity were investigated at several temperatures where the applied field was varied between 3 and -3 T. Several key results are obtained, such as: (a) the complete absence of exchange bias effect in sample S3; (b) the occurrence of nonconventional exchange bias effect in samples S2 and S1; (c) the sign-change of exchange bias field in sample S2; (d) the monotonic increase of coercivity with temperature above 100 K in all samples; (e) the existence of a critical temperature (100 K) at which the coercivity is minimum; (f) the surprising suppression of coercivity upon field-cooling; and (g) the observation of coercivity at all temperatures, even at 300 K. The results are discussed and attributed to the existence of spin glass clusters at the core-shell interface

⁵⁷Fe Mössbauer study of Ti⁴⁺-substituted Li₀․₅ ₍₁₊x ₎Cr₀․₁Fe₂․₄₋₁․₅xO₄ spinels

856-85957Fe Mössbauer effect (ME) was studied at 295K and 77K on the polycrystalline samples of the spinel oxide system Li₀․₅ ₍₁₊x ₎Cr₀․₁Fe₂․₄₋₁․₅xO₄ (x = 0.0 to 0.5) synthesized by double sintering ceramic technique. The chemical stoichiometry of the final products was ascertained by EDAX. The X-ray diffractometry (XRD) showed that all the samples were single-phase cubic spinels. The cell edge parameter, a (Å) for each composition was found by XRD-pattern indexing and using the Nelson-Riley method. The distribution of cations in the spinel was determined through XRD intensity analysis using the computer programme. The saturation magnetization for each composition was recorded using hysteresis loop tracer at the applied field of 4kOe. The Mössbauer spectra exhibit two Zeeman sextets due to different fields at tetrahedral (A) and octahedral (B) Fe³⁺ ions. The ME parameters are deduced using the NORMOS software and the observed hyperfine interaction parameters are explained in the light of cation distribution determined through XRD, magnetization and Mössbauer spectroscopic studies

Studies and characterizations of the Al Zarnkh meteorite

A newly fallen Sudanese meteorite named Al Zarnkh was investigated using room and liquid nitrogen temperature Mössbauer measurements, X-ray diffraction (XRD), and electron probe microanalysis (EPMA) in conjunction with energy dispersive X-ray microscopy. The Mössbauer spectra exhibited strong paramagnetic doublets with magnetic sextets. The doublets are assigned to olivine and pyroxene, while the magnetic sextets are assigned to troilite and kamacite. Based on microprobe analyses and textural studies, olivine is the most abundant phase and occurs as fine to medium grained laths both in the groundmass and in barred olivine chondrules. Both orthopyroxenes and clinopyroxenes are present and these tend to be granular. Plagioclase is an abundant interstitial groundmass phase. Chromites were detected in some groundmass olivine and are highly chromiumand iron-rich with no Fe3+ detected. The kamacite contains small amounts of Co. The mole fraction of the Fe end-member of olivine (fayalite) and orthopyroxene (ferrosilite) are found to be about 28% and 23%, respectively. These values are compared with that obtained from two chondritic meteorites. Based on these results, the studied meteorite is classified as an ordinary LL5 chondrite.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202