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1.
We present the preparation of massive Zn1???x Fe x O ternary oxides using the mechanical mill. The Fe atom is a particular dopant since it presents two different oxidation states which allow us to vary the starting materials: Fe2O3, $\upalpha $ -Fe or FeO. Parameters such as initial concentrations, atmosphere and milling times were varied. X-ray diffraction and 57Fe Mössbauer spectrometry (MS) were applied in order to analyze the structure evolution and iron incorporation in the wurtzite crystalline structure with milling time. At final stages, Fe atoms seem to be incorporated in the ZnO structure for those samples milled under Ar atmosphere. In all cases, two paramagnetic components, attributed to Fe atoms in both valence states, were observed by MS. 相似文献
2.
N. O. Khalifa H. M. Widatallah A. M. Gismelseed F. N. Al-Mabsali R. G. S. Sofin M. Pekala 《Hyperfine Interactions》2016,237(1):46
Single-phased nanocrystalline particles of pure and 10 % Ti 4+-doped perovskite-related YFeO 3were prepared via mechanosynthesis at 450°C. This temperature is ~150–350 °C lower than those at which the materials, in bulk form, are normally prepared. Rietveld refinements of the X-ray diffraction patterns reveal that the dopant Ti 4+ ions prefer interstitial octahedral sites in the orthorhombic crystal lattice rather than those originally occupied by the expelled Fe 3+ ions. Magnetic measurements show canted antiferromagnetism in both types of nanoparticles. Doping with Ti 4+ lowers the Néel temperature of the YFeO 3 nanoparticles from ~ 586 K to ~ 521 K. The Ti 4+-doped YFeO 3 nanoparticles exhibit enhanced magnetization and coercivity but less magnetic hyperfine fields relative to the un-doped nanoparticles. The 57Fe Mössbauer spectra show ~ 15 % of the YFeO 3 nanoparticles and ~22 of Ti 4+-doped YFeO 3 ones to be superparamagnetic with blocking temperatures < 78 K. The broadened magnetic components in the 57Fe Mössbauer spectra suggest size-dependent hyperfine magnetic fields at the 57Fe nuclear sites and were associated with collective magnetic excitations. The 57Fe Mössbauer spectra show the local environments of the Fe 3+ ions in the superparamagnetic nanoparticles to be more sensitive to the presence of the Ti 4+ ions relative to those in the larger magnetic nanoparticles. 相似文献
3.
Materials consisting of nanometer-sized magnetic particles are currently the subject of intensive research activities. Especially, much attention has been paid to their promising features for microwave magnetic properties. Well dispersed Fe3O4 nanoparticles of 30 nm have been synthesized by oxidization method with NaNO2, and the microwave magnetic properties of the composites have been studied. The real and imaginary part of relative permittivity remained low and nearly constant in the region of 0.1–18 GHz, respectively. As a result, the resin composites having a thickness of 2.0–3.2 mm, and containing 20 vol% Fe3O4 in the form of nanoparticles with an average diameter of 30 nm, exhibited excellent electromagnetic wave absorption properties in the frequency range of 4.5–12.0 GHz. 相似文献
4.
Haosheng Fei Mingyuan Gao Xicheng Ai Yangqiang Yang Tieqiao Zhang Jiacong Shen 《Applied Physics A: Materials Science & Processing》1996,62(6):525-528
Nano-sized -Fe2O3 particles coated with polar organic molecules have been studied using the Mössbauer spectroscopy method. The -Fe2O3 nanoparticles were prepared by the microemulsion method. The average particle size of the Fe2O3 particles is about 24 Å. Because the particle size is so small that the Mössbauer spectra of the -Fe2O3 samples only consist of a quadrupole-split central line. It was proved that the Isomer Shifts (DIS) and the Quadrupole Splitting (DQS) changed as the refluxing time prolongs and the refluxing temperature increases during the preparation of the Fe2O3 nanoparticles, which implied an enhancement of the surface electrofield gradient formed by the surface coated polar molecules during the refluxing process. 相似文献
5.
6.
M. I. Oshtrakh M. V. Ushakov V. A. Semionkin E. C. D. Lima P. C. Morais 《Hyperfine Interactions》2014,226(1-3):123-130
Study of maghemite nanoparticles, native and coated with DMSA as magnetic fluid for biomedical applications, was carried out using Mössbauer spectroscopy with a high velocity resolution at 295 and 90 K. The obtained results demonstrated differences in Mössbauer hyperfine parameters for uncoated and DMSA-coated nanoparticles which were related to the interactions of DMSA molecules with Fe3+? ions on maghemite nanoparticle’s surface. 相似文献
7.
H. Engelmann F. Mouahid I. Dézsi B. Molnár U. Gonser D. Siebert J. Dahlem F. Tuczek 《Applied Physics A: Materials Science & Processing》1989,48(3):211-217
Samples of the system LiNbO3-Fe2O3 prepared by water quenching and by the double-roller quenching method in the range up to 24 mol% Fe2O3 were investigated by Mössbauer and ESR spectroscopy. In the water quenched samples up to 11 mol% Fe2O3 only the Fe3+ and the Fe2+ valence states could be detected. The Fe2+ concentration decreased with increasing Fe2O3 content. Above 11 mol% Fe2O3 magnetically split Mössbauer spectra indicated the presence of Fe2O3 clusters. The isomer shift values of Fe3+ as a function of Fe2O3 concentration showed jumps at 6 and 11 mol% Fe2O3, whereas no significant changes could be detected in the quadrupole splitting values. The ESR data already exhibited the existence of isolated Fe3+ ions and of clusters with Fe-Fe distances less than 8 Å for the lowest Fe2O3 concentration. The cluster signal intensity increased with increasing Fe2O3 content. The roller quenched samples showed increased Fe2+ concentration as compared to the water quenched samples, which suggests that slow quenching results in iron oxidation and cluster formation. For low Fe2O3 concentrations a valence state change Fe3+Fe2+ can easily be obtained by heat treatments in various atmospheres, whereas for higher Fe2O3 contents (9.8 mol%) precipitations of-Fe (in reducing atmosphere) and Fe2O3 (in air) could be observed in addition to the valence state changes of a remaining part of dissolved Fe ions. On the basis of the obtained results a model was suggested for the unusual behaviour of the lattice parameters observed in LiNbO3-Fe2O3. 相似文献
8.
Complete replacement of copper by iron in RBa2Cu3O7 leads to RBa2Fe3O8 (R=Y, rare earth). Mössbauer spectroscopy measurements of57Fe and151Eu in RBa2Fe3O8 (R=Y, Eu, Ho, Er) at temperatures 4.2–800 K have been performed. Some of the spectra reveal two inequivalent iron sites, probably corresponding to iron in the Fe(2) site (fivefold oxygen coordination) and in the Fe(1) site (octahedral oxygen coordination). In all compounds the iron moments order antiferromagnetically at the same Néel temperatureT
N720 K. The151Eu Mössbauer spectra of EuBa2Fe3O8 show that the Eu ion is trivalent and exposed to a small exchange field from the iron sublattices. 相似文献
9.
M. I. Oshtrakh M. V. Ushakov B. Senthilkumar R. Kalai Selvan C. Sanjeeviraja I. Felner V. A. Semionkin 《Hyperfine Interactions》2013,219(1-3):7-12
The nanocrystalline NiFe2O4 particles prepared by solution combustion synthesis technique using different fuels such as ethylene-diamine-tetra-acetic acid (NA sample) and urea (NB sample) were studied using magnetic measurement and 57Fe Mössbauer spectroscopy with a high velocity resolution. The temperature dependence of magnetization is different for the two samples. Mössbauer spectra demonstrate the necessity to use more than two magnetic sextets, usually used to fit the NiFe2O4 nanoparticles spectra. Evaluation of the different local microenvironments for Fe in both tetrahedral (A) and octahedral (B) sites, caused by different Ni2?+? occupation of octahedral sites, demonstrates at least five different local microenvironments for both A and B sites. Therefore, the Mössbauer spectra were fitted by using ten magnetic sextets which are related to the spread 57Fe location in octahedral and tetrahedral sites. 相似文献
10.
《Physica B+C》1979,96(1):103-110
A slowly cooled sample of the ferrimagnetic spinel MgFe2O4 has been studied with 57Fe Mössbauer spectroscopy over a wide temperature range both with and without high magnetic fields. The observed temperature dependence of the A and B site hyperfine parameters is discussed. Conclusions about the spin structure, the magnetic exchange interactions and the supertransferred hyperfine fields are presented. 相似文献
11.
With the advent of Fe–As based superconductivity it has become important to study how superconductivity manifests itself in details of 57Fe Mössbauer spectroscopy of conventional, Fe-bearing superconductors. To this end, the iron-based superconductor Lu2Fe3Si5 has been studied by 57Fe Mössbauer spectroscopy over the temperature range from 4.4 K to room temperature with particular attention to the region close to the superconducting transition temperature (Tc=6.1 K). Consistent with the two crystallographic sites for Fe in this structure, the observed spectra appear to have a pattern consisting of two doublets over the whole temperature range. The value of Debye temperature was estimated from temperature dependence of the isomer shift and the total spectral area and compared with the specific heat capacity data. Neither abnormal behavior of the hyperfine parameters at or near Tc, nor phonon softening were observed. 相似文献
12.
The powders of X20Cr13 steel were subjected to ball milling process in a planetary ball mill. X-ray diffraction and Mössbauer spectroscopy studies revealed the refinement of the structure of this steel down to a nanocrystalline range practically without any phase transformations. Both techniques allowed to detect the alloyed ferrite as well as residual content of iron containing M23C6-type carbide, which was dissolved into the ferrite during milling. Hyperfine magnetic fields in ball milled steel samples did not differ significantly from those for the bulk steel disc. 相似文献
13.
The room temperature Mössbauer spectra of 57Fe were measured for nanocrystalline iron-based solid solutions Fe 1?x Re x , prepared by mechanical alloying with x in the range 0.01 ≤ x ≤ 0.04. The obtained data were analysed in terms of the binding energy E b between two rhenium atoms in the Fe-Re system. The extrapolated value of E b for x = 0 was used for computation of enthalpy of solution of rhenium in iron. The result was compared with that resulting from the cellular atomic model of alloys by Miedema as well as with value, derived from proper data for Fe-Re solid solutions obtained by melting in an arc furnace. From the comparison it follows that our findings are in agreement with the Miedema’s model predictions and previous Mössbauer studies. 相似文献
14.
《Solid State Communications》1987,64(5):635-638
Guided by the occupancies and iron magnetic moments μ3, 57Fe Mössbauer parameters of Y2Fe14B at 250K, and in turn for other temperatures, of the sublattices of iron were deduced. Plots of μ(T) in reduced coordinates, through the established correlation between hyperfine field Hn and μ, show that the corresponding state of different iron sites is different and all experimental points fall below Brillouin function. The relation between exchange integral deviation parameter Δ and standard deviation of Fe-Fe interatomic distances S is linear, indicating electrostatic nature of exchange interactions between spins in neighboring atoms. It is inclined to the view that fluctuations of exchange integral is responsible for low Tc of R2Fe14B. 相似文献
15.
《Journal of magnetism and magnetic materials》2001,224(2):143-152
Nd60Fe30Al10 alloys were rapidly quenched by the melt-spinning technique with different wheel surface speeds ranging from 5 to 30 m/s. The microstructure and the magnetic properties were strongly dependent on the quenching rate. A high quenching rate led to an amorphous structure with a low coercivity at room temperature, while a mixture of amorphous and crystalline phases was found after melt-spinning at 5 m/s, which exhibited hard magnetic properties at room temperature. For both the ribbons melt-spun at 5 and 30 m/s respectively, coercivity increased with decreasing temperature and reached a maximum at around 50 K. Maximum magnetization at 10 T increased dramatically at low temperature. Our magnetic study has shown that the presence of crystalline Nd was responsible for the increase of magnetization and the decrease of coercivity, as Nd became magnetically ordered at low temperatures. The Mössbauer study has shown that the magnetic microstructures of melt-spun ribbons were not uniform, as the spectra needed to be fitted by magnetic and non-magnetic components. 相似文献
16.
E. Kuzmann S. Stichleutner A. Sápi Z. Klencsár M. I. Oshtrakh V. A. Semionkin S. Kubuki Z. Homonnay L. K. Varga 《Hyperfine Interactions》2013,215(1-3):63-67
Stress field and magnetic field annealed FINEMET ribbons were investigated by 57Fe Mössbauer spectroscopy, magnetic and XRD methods. The change in relative areas of the 2nd and 5th lines in the Mössbauer spectra indicated significant variation in magnetic anisotropy due to the different annealing. High velocity resolution Mössbauer spectroscopy was also used to control the model applied for the evaluation of Mössbauer spectra. A correlation was found between the permeability and the magnetic anisotropy of the annealed FINEMET samples. This can be applied to predict production parameters of FINEMET ribbons with more favorable soft magnetic properties for technological applications. 相似文献
17.
Kwang Pyo Chae Woo Hyun Kwon Young Bae Lee Seo Wook Paik Sung Ho Lee 《Hyperfine Interactions》1999,122(3-4):269-275
The Fe‐doped system Cu0.9Ge0.9Fe0.2O3 has been investigated by means of X‐ray diffractometry, Mössbauer spectroscopy and superconducting quantum interference device. The structure of this system is orthorhombic and the lattice constants are a=4.784 Å, b=8.472 Å and c=2.904 Å, respectively. Magnetic measurements confirm that the spin‐Peierls transition appears in our sample at about 12 K, which is near to the spin‐Peierls transition temperature (T sp) 14 K of pure CuGeO3 system. The Mössbauer spectrum shows the superposition of two Zeeman sextets and a broad central line due to Fe3+ ions from room temperature to 4.2 K. The Mössbauer parameters show a discontinuity near T sp. The jump of the magnetic hyperfine field at temperatures lower than T sp means increasing of the superexchange interaction among the magnetic ions. The jump of the quadrupole splitting and the isomer shift values could be interpreted as due to decrement in symmetry of lattice sites and spontaneous thermal contraction. 相似文献
18.
Jean-Claude Jumas Manfred Womes Ricardo Alcántara Pedro Lavela José L. Tirado 《Hyperfine Interactions》2008,183(1-3):1-5
Transmission Mössbauer spectroscopy and CEMS are powerful tools to study the changes in which iron-containing active materials of conversion electrodes are involved during lithium cell charge and discharge. The usual spectrum of pristine CoFe2O4 spinel with two sextets ascribable to Fe3?+? ions in both tetrahedral and octahedral environments, changes dramatically after cell discharge to 0 V vs. Li, and can be interpreted as the result of iron reduction to the metallic state in the form of superparamagnetic metal nanoparticles dispersed in a Li2O matrix. After cell charge to 3 V, the MS of the pristine sample is not recovered. Instead, two new doublets are visible with IS ascribable to Fe3?+? ions. 57Fe CEMS evidences the different environment of iron atoms in the surface of the nanodispersed material found in the used electrodes. 相似文献
19.
Many useful properties of magnetic multilayers depend on the coupling between the ferromagnetic layers. The coupling often oscillates with the thickness of non-magnetic spacer layers: it is ferro- or antiferromagnetic or even non-collinear near a critical thickness. We investigated the magnetron-sputtered Fe/FeSi multilayers with spacer thickness around 1.7 nm by means of Conversion Electron Mössbauer Spectroscopy with oblique incidence of the γ beam in order to gain information on the orientation of the local magnetic moments in the multilayer plane. The results show that the local moments make an angle of 45°–50° with the direction of the remanent magnetization. This is consistent with strong biquadratic coupling which in turn is expected at this spacer thickness from our magnetic measurements. An analysis of the distribution ofB hf corresponding to different numbers of n.n. Si atoms in the bcc Fe structure points to weak diffusion of Si through the Fe/FeSi interface characterized by a diffusion length of about twice the substrate roughness. 相似文献
20.
M. I. Oshtrakh E. V. Petrova V. I. Grokhovsky V. A. Semionkin 《Hyperfine Interactions》2008,186(1-3):61-68
Mössbauer spectroscopy with high velocity resolution was used to study of 11 ordinary chondrites from L and H chemical groups. Mössbauer 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 Mössbauer 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 Mössbauer spectra of bulk chondrite samples. 相似文献