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1.
The structural changes of near-equiatomic α-FeCr alloys, ground in a vibratory mill in vacuum and in argon, were followed as a function of milling time. An amorphous phase forms in both cases but at a much faster rate when milling in argon than when milling in vacuum. Amorphisation by ball-milling of α-FeCr alloys is deduced to be an intrinsic phenomenon which is however speeded-up by oxygen. The amorphous phase crystallizes into a bcc Cr-rich phase and a bcc Fe-rich phase when annealed for short times.  相似文献   

2.
Mössbauer and infrared studies were made on samples of the ferrite system Co1–xCdxFe2O4 x=0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1. Mössbauer spectra were taken at room temperature. The spectra of the samples withx0.7 showed well defined Zeeman patterns and they have been analyzed with two components, one due to A-site Fe3+ ions, and the other due to B-site Fe3+ and Fe2+ ions. The pattern due to B-site appeared to be composite and an explanation is given. The spectra withx=0.9 and 1 showed only a quadrupole splitting. The effect of cadmium substitution on the various hyperfine interactions has been discussed and the cationic distribution has been deduced for all values ofx. Far infrared spectra of the ferrite samples in the range 200–700 cm–1 were reported. Four bands were observed: the high frequency bandv 1 is assigned to tetrahedral complexes, and the low frequency bandv 2 to octahedral complexes, a small bandv 3 is due to Co2+-O2– complexes andv 4 is assigned to the lattice vibration of the system. The splitting occurred in thev 1 andv 2 bands atx=0.9 and inv 2 atx=1, indicating the presence of Fe2+ ions in octahedral sites.  相似文献   

3.
57Fe Mössbauer spectroscopy is used to study neutron irradiation induced changes in the short-range order of Fe73.5Nb3Cu1Si13.5B9 alloy. The samples are investigated in both amorphous and nanocrystalline states. Neutron irradiation leads to an increase of the standard deviation of a hyperfine field distribution (HFD), implying rearrangement of the atoms towards disordering. Simultaneously, changes in the average value of the hyperfine field and a net magnetic moment position occur as a consequence of a spin reorientation, atom mixing and microscopic stress centres which are introduced by neutron irradiation.  相似文献   

4.
High-purity Fe powder was mechanically milled under argon at ambient temperature using an SPEX 8000 mill. The local atomic and magnetic structure was studied using57Co/Fe Mössbauer and111In/Cd perturbed angular correlations (PAC) spectroscopies. After 32 hours of milling, X-ray diffraction revealed effective grain diameters of 18 nm and energy-dispersive X-ray analysis indicated a Cr impurity concentration of 5%, presumably introduced by mechanical attrition of steel ball bearings used for milling. In addition to a spectral component very similar to bulk iron metal, the Mössbauer spectra exhibited hyperfine field shifts attributed to the Cr impurities. PAC spectra on Fe milled for 5 h, with no contamination, exhibited two components: (1) A slightly broadened magnetic interaction attributed to interior, defect-free sites of In/Cd probes with a mean hyperfine field slightly greater than in macroscopic grains. The defect-free site fraction grew appreciably during milling, even though In is essentially insoluble in Fe. (2) An indistinct signal due to mixed magnetic and quadrupole interactions attributed to probes at surface or other defect sites.  相似文献   

5.
A non-thermal route to oxide nanocomposites by mechanochemical redox reactions in the ??-Fe2O3 + SnO system is presented. The important impact of the work, from the methodology point of view, is the combined application of 57Fe and 119Sn Mössbauer spectroscopies to the study of the mechanically induced redox processes, resulting in the reduction of ??-Fe2O3 and the oxidation of SnO. In addition, the obtained product was characterized by X-ray diffraction and transmission electron microscopy.  相似文献   

6.
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   

7.
8.
Our investigations on substitutional and interstitial Fe in the group IV semiconductors, from 57Fe Mössbauer measurements following 57Mn implantation, have been continued with investigations in 3C-SiC. Mössbauer spectra were collected after implantation and measurement at temperatures from 300 to 905 K. Following comparison with Mössbauer parameters for Fe in Si, diamond and Ge, four Fe species are identified: two due to Fe in tetrahedral interstitial sites surrounded, respectively, by four C atoms (Fei.C) or four Si atoms (Fei,Si) and two to Fe in (or close to) defect free or implantation damaged substitutional sites. An annealing stage at 300–500 K is evident. Above 600 K the Fei,Si fraction decreases markedly, reaching close to zero intensity at 905 K. This is accompanied by a corresponding increase in the Fei,C fraction.  相似文献   

9.
57Fe (1%) doped SrCoO3 obtained by high-pressure method, has been investigated by magnetization and Mössbauer spectroscopy studies (MS) in the temperature range 4.2 K to 300 K. The ferromagnetic ordering temperature T C obtained is 272(2) K. Isothermal magnetization curves have been measured at various temperatures, from which the saturation moments (M sat) have been deduced. The 57Fe MS spectra display standard six-line patterns with an isomer shift typical of Fe3?+? and a very small quadrupole splitting (QS = 0.14(1) mm/s above T C). The magnetic hyperfine field at 4.2 K is 276(1) kOe. The temperature dependencies of the iron hyperfine field and M sat (1.83 µ B at 5 K) are almost identical. This shows that the Fe3?+? is replacing Co4?+?, both of the same electronic configuration. They also interact similarly, namely the Fe–Co exchange is almost identical to the Co–Co exchange.  相似文献   

10.
Samples of SnO2 doped with different amount of Fe (10–20%) and Sb (5–25%) were prepared by sol–gel method. Room temperature ferromagnetism was found to increase as a result of co-doping with Sb, as compared to SnO2 doped only with Fe. 57Fe Mössbauer spectra of almost all samples exhibited two paramagnetic doublets and a small subspectrum referring to magnetic relaxation at room temperature. Only the samples Sn0.65Fe0.2Sb0.15O2???δ and Sn0.85Fe0.1Sb0.05O2???δ with 4 h long annealing time showed well developed sextets and larger magnetic coercivity compared to that of the other samples. The sextet observed was considered to be due to precipitates like Sn doped α-Fe2O3. The results suggest that the origin of the magnetic interactions is enhanced by the presence of magnetic defects, which can interact with the iron ions by free carrier electrons. For the sample with precipitates, the grain boundary defects may play an important role of enhanced ferromagnetism.  相似文献   

11.
The present work reports results of the 57Fe Mössbauer measurements on AgFeO2 powder sample recorded at various temperatures including the points of both magnetic phase transitions. The 57Fe Mössbauer spectra of AgFeO2 measured in the paramagnetic range (T > T N1) consist of one quadrupole doublet with rather high quadrupole splitting of Δ300K = 0.66 ± 0.01 mm/s for Fe3+ ions. In order to predict the sign of electric field gradient (EFG) at 57Fe nuclei, we calculated the lattice contribution to the electric field gradient (EFG) at 57Fe nuclei, which emphasized the importance of the dipolar contributions, with resultant oxygen polarizabilities in the range of α O = 0.83 Å3, in agreement with the results obtained previously for other delafossite-like oxides. In the temperature range of T N2 < T < T N1, Mössbauer spectra gave clear evidence for the existence of a distribution of the hyperfine magnetic fields H hf at 57Fe nuclei. We present the results of a model fitting of the spectra based on an assumption of the cycloid magnetic structure of AgFeO2 at T < T N2. The obtained data were analysed in comparison with published data on Mössbauer studies of oxide multiferroics.  相似文献   

12.
Nanosize zinc ferrite particles, prepared by nitrate method, were investigated by XRD, TEM, 57Fe Mössbauer spectroscopy and VSM. The average particle size in this system varies from 10 to 62 nm as the sintering temperature increases from 300°C to 1,000°C. The lattice parameters in this system are almost constant at a value of ~8.41 Å. The Mössbauer spectra of all the sintered samples show a single doublet. The Mössbauer hyperfine parameters show little change with the change of sintering temperature. The doublets are ascribed to the presence of superparamagnetism in this system, which is also corroborated by the VSM measurements.  相似文献   

13.
Soft magnetic nanocrystalline alloys have attracted great fundamental interest in recent years due to their two-phase structural and magnetic behaviour. We review first the reliability of the fitting procedures of spectra obtained by 57Fe Mössbauer spectrometry which is a very efficient tool to investigate such materials. Then, we report the common features which characterise the temperature dependence of Mössbauer spectra; the hyperfine field temperature dependence of both the crystalline grains and the intergranular phase is discussed for different crystalline fractions in order to model the magnetic behaviour of the nanocrystalline alloys.  相似文献   

14.
Ion implantation provides a precise method of incorporating dopant atoms in semiconductors, provided lattice damage due to the implantation process can be annealed and the dopant atoms located on regular lattice sites. We have undertaken 57Fe emission Mössbauer spectroscopy measurements on GaAs and GaP single crystals following implantation of radioactive 57Mn?+? ions, to study the lattice sites of the implanted ions, the annealing of implantation induced damage and impurity–vacancy complexes formed. The Mössbauer spectra were analyzed with four spectral components: an asymmetric doublet (D1) attributed to Fe atoms in distorted environments due to implantation damage, two single lines, S1 assigned to Fe on substitutional Ga sites, and S2 to Fe on interstitial sites, and a low intensity symmetric doublet (D2) assigned to impurity–vacancy complexes. The variations in the extracted hyperfine parameters of D1 for both materials at high temperatures (T?> 400 K) suggests changes in the immediate environment of the Fe impurity atoms and different bonding mechanism to the Mössbauer probe atom. The results show that the annealing of the radiation induced damage is more prominent in GaAs compared to GaP.  相似文献   

15.
Sandstones from the Free State province in South Africa have been mined and processed mainly by small scale and artisanal miners in the rural areas. In the present investigation basic fire proof and water absorption tests, X-ray and γ-ray based characterisation techniques were used to study the sandstones. The collected samples were grouped according to their apparent colour in day light conditions and the elemental analysis showed the presence of a high amount of oxygen (>52%) and silicon (>38%) with Mn, Al, Fe and Ca as major elements in proportions related to the colour distribution of the various sandstones. The uniaxial compressive stress was found to be the highest (56 MPa) for the greyish sandstone and the lowest (8 MPa) for the white sandstone sample, also associated with the lowest (Al+Fe)/Si value of 0.082. The humidity test showed that the 6 % water absorption was lower than the recommended ASTM value of 8 %. The sandstone samples were also subjected to various high temperatures to simulate possible fire conditions and it was found that the non alteration of the mineral species might be one of the reasons why the sandstones are regarded as the most refractory amongst the building materials typically used. Mössbauer spectroscopy revealed that iron is present in all the sandstones, mainly as Fe3?+? with the black sandstone showing an additional presence of 3 % Fe2?+? indicating that a higher iron content coupled to higher silicon content, contributes to an increase in the uniaxial compressive strength.  相似文献   

16.
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   

17.
YFexAl12−x in the composition range 4.4⩽x⩽5 was prepared by induction melting followed by annealing in vacuum at 1270 K. Magnetization data below 150 K show complex magnetic behaviour dependent on applied field, composition and temperature. The transition temperature Tc, corresponding to the main maximum of the magnetization vs. temperature curves and below which magnetic interactions are observed for a significant fraction of the Fe atoms in the Mössbauer spectra, decreases from 180 K for x=4 down to 100 K for 4.2⩽x⩽4.7 and rises again up to 160 K for x=5. The analysis of the spectra obtained at 5 K is consistent with full occupation of the 8f sites by Fe atoms and sharing of the 8j sites by Fe and Al as deduced from the Rietveld analysis of X-ray powder diffraction data. The Mössbauer spectra further show a dependence of magnetic hyperfine fields and isomer shifts on the crystallographic site and on the number of the Fe nearest neighbours similar to that observed in UFexAl12−x (4⩽x⩽6) and RFexAl12−x (R=Y, Lu, x=4, 4.2). The magnetic properties of the UFexAl12−x and YFexAl12−x series are compared and the magnetic interactions between the different Fe sublattices are discussed.  相似文献   

18.
57Fe Mössbauer measurements have been perforned at the first time on iron nitrides, FeNx(x>0.5), films prepared by rf sputtering and the measurements for γ-FeN0.09, γ'-Fe4N, ε-Fe2–3N and ζ-Fe2N have been also performed. Two new phases for x>0.5 have been identified: One has a ZnS-type structure denoted by γ" Another phase is denoted by γ''' in which iron atoms constitute a fcc lattice but the details of occupation sites of nitrogen atoms are not yet clear. The isomer shift of γ" relative to α-Fe at 300 K is rather small in comparison with that of other well known nitrides. The roam temperature Mössbauer spectra of γ''' consist of a sum of two doublets. Mössbauer spectra of γ" at 10 K do not indicate magnetically split pattern, but those of γ''' show magnetically split patterns at 10 K with the hyperfine fields of 30 T and 48 T, respectively. The component of 48 T is due to oxides, not due to nitrides.  相似文献   

19.
The ferrites Mg0.9Mn0.1Cr x Fe2?x O4 ( The ferrites Mg0.9Mn0.1Cr x Fe2−x O4 () were prepared using the conventional double sintering method. The XRD showed that the samples maintain a single spinel cubic phase. The M?ssbauer measurements were carried out at room and liquid nitrogen temperatures. From the area ratios of the A and B sites, it was found that the Fe cation population of the A and B sites decreases in proportion to Cr concentration. The contact hyperfine fields at the A and B sites were found to decrease with increasing Cr contents. This was found to be in approximate agreement with the results of magnetization measurement. The distributions of Mg and Mn cations versus Cr concentration were also determined using the M?ssbauer and magnetization results. The Curie temperatures were determined and found to agree with the reported values. As the Cr contents increases the relative magnetization, was found to increase at low temperatures and decreases at higher temperatures.  相似文献   

20.
Bulletin of the Russian Academy of Sciences: Physics - Zn1–x Fe x O nanocrystalline solid solutions (x = 0, 0.025, 0.05) with wurtzite structure and ferromagnetic properties at room...  相似文献   

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