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1.
The linear and nonlinear low field AC susceptibilities of Zn0.75Co0.25Fe0.5Cr1.5O4 show peaks due to non-critical contributions, which mask the peak due to spin glass ordering. They extend into the region of temperatures in which Mössbauer spectra do not show any magnetic component. When a DC field of 200 Oe suppresses the non-critical contributions, peak due to spin glass ordering is clearly visible. The spin glass ordering is thus shown to be a thermodynamic transition. The critical exponent is found to fall within the range found using other spin glasses. Mössbauer spectra in zero fields provide TSG, which agrees with the peak temperature of AC susceptibilities in the absence of non-critical contributions. 〈SZ〉 determined using Mössbauer spectra does not show any anomaly. In the presence of a field of 5 T, the spectra show SG ordering at 4.2 K, which converts into ferrimagnetic ordering at higher temperatures. 相似文献
2.
The xZnO-(1−x)α-Fe2O3 nanoparticles system has been obtained by mechanochemical activation for x=0.1, 0.3 and 0.5 and for ball milling times ranging from 2 to 24 h. Structural and morphological characteristics of the zinc-doped hematite system were investigated by X-ray diffraction (XRD) and Mössbauer spectroscopy. The Rietveld structure of the XRD spectra yielded the dependence of the particle size and lattice constant on the amount x of Zn substitutions and as function of the ball milling time. The x=0.1 XRD spectra are consistent with line broadening as Zn substitutes Fe in the hematite structure and the appearance of the zinc ferrite phase at milling times longer than 4 h. Similar results were obtained for x=0.3, while for x=0.5 the zinc ferrite phase occurred at 2 h and entirely dominated the spectrum at 24 h milling time. The Mössbauer spectra corresponding to x=0.1 exhibit line broadening as the ball milling time increases, in agreement with the model of local atomic environment. Because of this reason, the Mössbauer spectrum for 12 h of milling had to be fitted with two sextets. For x=0.3 and 12 milling hours, the Mössbauer spectrum reveals the occurrence of a quadrupole-split doublet, with the hyperfine parameters characteristic to zinc ferrite, ZnFe2O4. This doublet clearly dominates the Mössbauer spectrum for x=0.5 and 24 h of milling, demonstrating that the entire system of nanoparticles consists finally of zinc ferrite. As ZnO is not soluble in hematite in the bulk form, the present study clearly demonstrates that the solubility limits of an immiscible system can be extended beyond the limits in the solid state by mechanochemical activation. Moreover, this synthesis route allowed us to reach nanometric particle dimensions, which would make the materials very important for gas sensing applications. 相似文献
3.
Bae Soon Son Sam Jin Kim Younghun Jo Myung-Hwa Jung Bo Wha Lee Chul Sung Kim 《Journal of magnetism and magnetic materials》2008
The sample of FeSc2S4 was prepared by solid reaction method. The crystallographic structure and the magnetic properties of the fabricated compound were investigated by X-ray, and superconducting quantum interference device (SQUID) magnetometer and Mössbauer spectroscopy. The polycrystalline FeSc2S4 confirmed the normal cubic spinel structure (space group Fd3m). The lattice constants a0 and anion parameter u are 10.519 Å and 0.255, respectively. The Mössbauer spectroscopy has been studied for the FeSc2S4 at various temperatures, ranging from 4.2 K to room temperature. The spectra consist of two doublets at 4.2 K while a single line at room temperature. It is noticeable that the Mössbauer spectra of two doublet patterns with large electric quadrupole splitting (ΔEQ) remain over the Néel temperature. Those are interpreted as a result of large electric quadrupole interaction compared to magnetic dipole interaction. The magnetic susceptibility measurements were performed with a SQUID magnetometer for temperatures 2<T<320 K, in external fields up to 5 kOe. Magnetic behavior shows antiferromagnetic behavior and the magnetic superexchange interactions between the Fe ions are weakly antiferromagnetic. The paramagnetic susceptibilities follow Curie–Weiss (CW) law with CW temperature ΘCW=−100 K, and frustration parameter f=−ΘCW/TN is of the order of 1000. We conclude that two sublattices are coupled antiferromagnetically, leading to strong frustration effects. 相似文献
4.
A. Bhattacharjee P.J. van Koningsbruggen Joel S. Miller 《Journal of Physics and Chemistry of Solids》2008,69(11):2713-2718
The 57Fe Mössbauer spectroscopy of mononuclear [Fe(II)(isoxazole)6](ClO4)2 has been studied to reveal the thermal spin crossover of Fe(II) between low-spin (S=0) and high-spin (S=2) states. Temperature-dependent spin transition curves have been constructed with the least-square fitted data obtained from the Mössbauer spectra measured at various temperatures between 84 and 270 K during a cooling and heating cycle. This compound exhibits an unusual temperature-dependent spin transition behaviour with TC(↓)=223 and TC(↑)=213 K occurring in the reverse order in comparison to those observed in SQUID observation and many other spin transition compounds. The compound has three high-spin Fe(II) sites at the highest temperature of study of which two undergo spin transitions. The compound seems to undergo a structural phase transition around the spin transition temperature, which plays a significant role in the spin crossover behaviour as well as the magnetic properties of the compound at temperatures below TC. The present study reveals an increase in high-spin fraction upon heating in the temperature range below TC, and an explanation is provided. 相似文献
5.
M. Pissas V. Psycharis D. Stamopoulos G. Papavassiliou Y. Sanakis A. Simopoulos 《Solid State Communications》2006,137(12):668-672
We studied by Mössbauer spectroscopy the Na0.82CoO2 compound using 1% 57Fe as a local probe which substitutes for the Co ions. Mössbauer spectra at T=300 K revealed two sites which correspond to Fe3+ and Fe4+. The existence of two distinct values of the quadrupole splitting instead of a continuous distribution should be related with the charge ordering of Co+3, Co+4 ions and ion ordering of Na(1) and Na(2). Below T=10 K part of the spectrum area, corresponding to Fe4+ and all of Fe3+, displays broad magnetically split spectra arising either from short-range magnetic correlations or from slow electronic spin relaxation. 相似文献
6.
Thermo-gravimetric, differential scanning calorimetry and comprehensive 57Fe Mössbauer spectroscopy studies of amorphous and crystalline ferromagnetic glass coated (Co0.2Fe0.8)72.5Si12.5B15 micro-wires have been recorded. The Curie temperature of the amorphous phase is TC(amorp) ∼730 K. The analysis of the Mössbauer spectra reveals that below 623 K the easy axis of the magnetization is axial-along the wires, and that a tangential or/and radial orientation occurs at higher temperatures. At 770 K, in the first 4 hours the Mössbauer spectrum exhibits a pure paramagnetic doublet. Crystallization and decomposition to predominantly α-Fe(Si) and Fe2B occurs either by raising the temperature above 835 K or isothermally in time at lower temperatures. Annealing for a day at 770 K, leads to crystallization. In the crystalline material the magnetic moments have a complete random orientation. After cooling back to ambient temperature, both α-Fe(Si) and Fe2B in the glass coated wire show pure axial magnetic orientation like in the original amorphous state. The observed spin reorientations are associated with changes in the stress induced by the glass coating. 相似文献
7.
Lijun Zhao Zhaoyang Han Hua Yang Lianxiang Yu Yuming Cui Weiqun Jin Shouhua Feng 《Journal of magnetism and magnetic materials》2007
Mössbauer spectra and magnetic measurement of Ni0.7Mn0.3Gd0.1Fe1.9O4 ferrite were investigated by Oxford MS-500 Mössbauer spectrometer and superconducting quantum interference device (SQUID) magnetometer with a field 5 T. Ni0.7Mn0.3Gd0.1Fe1.9O4 nanoparticles have a considerable coercivity of 1040 Oe when the test temperature is reduced to 2 K. Mössbauer spectra show that Ni0.7Mn0.3Gd0.1Fe1.9O4 nanoparticles exhibit superparamagnetism at room temperature and ferrimagnetism at 77 K. 相似文献
8.
The crystallographic and magnetic properties of low aluminum doped lithium cobalt titanium ferrites, Li0.5Co0.2Ti0.2AlxFe2.1−xO4(0.0≤x≤0.5), in the scope of spinel structure and ferrimagnetic property were investigated. Ferrites were doped with aluminum in the range of 0.0–0.5 and were synthesized by using the conventional ceramic methods. Using X-ray diffraction and Mössbauer spectroscopy, we confirmed the formation of crystallized particles. All of the samples showed a single phase with a spinel structure, and the lattice parameters linearly decreased as the doped aluminum content was increased. The particle size of the samples also decreased as the doped aluminum content increased. Until x=0.4 in Li0.5Co0.2Ti0.2AlxFe2.1−xO4, the Mössbauer spectra could be fitted with two Zeeman sextets, which is the typical spinel ferrite spectra of Fe3+ with A- and B-sites. However, for x=0.5, the Mössbauer spectrum could be fitted with two Zeeman sextets and one doublet. From the variation of the Mössbauer parameters and the absorption area ratio, the cation distributions were determined. The magnetic behavior of the samples showed that an increase in the aluminum contents led to a decrease in the saturation magnetization, whereas the coercivity decreased until x=0.4 and then increased. The minimum coercivity was 52.4 Oe at x=0.4 in Li0.5Co0.2Ti0.2AlxFe2.1−xO4. 相似文献
9.
Results obtained by means of the emission Mössbauer spectroscopy in CoO and Co3O4 systems kept under relatively high oxygen pressure (air close to the normal pressure) are reported. Broadening of the 14.4-keV 57Fe Mössbauer line due to the diffusion of iron atoms in CoO has been investigated in the temperature range between 1275 and 1450 K. The excess of the linewidth caused by diffusive motions obeys the Arrhenius law with the activation energy of 1.86(8) eV. Mixed valence oxide Co3O4 was examined vs. temperature. Measurements were performed from the room temperature till 1073 K. Tetrahedrally coordinated iron impurities in the Co3O4 host lattice are in the high spin trivalent state despite that parent Co is divalent. The anharmonic contribution to the lattice vibrations at high temperatures was observed and analyzed for both CoO and Co3O4. 相似文献
10.
Spinel ferrite CuFe2O4 and solid solution of Cu1−xZnxFe2−yGayO4 with 0.0?x?0.5 are synthesized through the usual ceramic method. X-ray diffraction measurements confirm the presence of single-phase tetragonal structure with c/a>1for CuFe2O4 and compositions with x?0.1. The formation of the tetragonal phase in these samples is attributed to the presence of the cooperative Jahn–Teller Cu ion at the octahedral B-site in the spinel lattice. At the compositional parameter x?0.2, tetragonal-to-cubic transformation occurred and the lattice parameter a for the cubic unit cell is found to decrease with increasing Zn content x. 57Fe Mössbauer measurements at 293 K for these compounds reveal superparamagnetic phase for samples with 0.0?x?0.2. In contrast, Mössbauer spectra at 12 K for these materials show well ordered spectra where, the cation distribution and the hyperfine parameters are determined. 相似文献
11.
Ali Ghasemi Andrea Paesano Jr. Carla Fabiana Cerqueira Machado 《Journal of magnetism and magnetic materials》2012
Co1−xNix/2Srx/2Fe2O4 (x=0–0.5 in steps of 0.1) ferrite nanoparticles have been synthesized at room temperature, without calcination, using a reverse micelle process. The site preference was determined by Mössbauer spectroscopy at 300 K. The hyperfine parameters were obtained, for the whole series of solid solutions. For the X≤0.20 samples, the spectra were fitted with two discrete sextets and for the X>0.20 samples, a magnetic hyperfine field distribution and a doublet were also imposed in the fit procedure. Hysteresis loops were measured using a superconducting quantum interference device magnetometer at 2 K and 300 K. The results indicate that the relative decrease in saturation magnetization of nanoparticles compared to the submicron particles could be attributed to a surface spin termination and disorder. Magnetic dynamics of the nanoparticles was studied by the measurement of ac magnetic susceptibility versus temperature at different frequencies and it is found that the results are well described by the Vogel–Fulcher model. 相似文献
12.
El?bieta Jartych Mariusz Mazurek Dionizy Czekaj 《Journal of magnetism and magnetic materials》2010,322(1):51-55
X-ray diffraction and Mössbauer spectroscopy were applied as complementary methods to investigate the structure and hyperfine interactions in the series of Bim+1Ti3Fem−3O3m+3 Aurivillius compounds with m=4, 6, 7 and 8. Samples were synthesized by the solid-state sintering method at various temperatures. As X-ray diffraction analysis proved, the compounds formed single phases at temperature above 993 K. Mössbauer studies have confirmed diffraction measurements. Compounds synthesized at 993 K contained residual hematite, however these sintered at elevated temperatures were single-phased materials. Room-temperature Mössbauer spectra of Bim+1Ti3Fem−3O3m+3 compounds revealed their paramagnetic properties, what is consistent with the literature data concerning the Néel temperature of these ceramics (TN is smaller than room temperature). Detailed analysis of MS spectra allowed to state that iron ions may occupy both tetrahedral and octahedral sites in the crystallographic lattice of Aurivillius compounds. 相似文献
13.
Charge disproportionation in La0.5Ca0.5FeO3−δ perovskite has been detected by zero-field Mössbauer spectra from 20 K to room temperature. On the basis of the parameters of center shifts and hyperfine fields, Mössbauer spectra identified that the iron ionic states are Fe3+ and Fe5+ below 150 K, Fe3+, Fe4+ and Fe5+ in the intermediate temperature region, as well as Fe3+ and Fe4+ above 220 K. At low temperatures, the system exhibits a cluster-glass-like state resulting from competition between antiferromagnetic interaction of Fe3+–Fe3+ and ferromagnetic interaction of Fe3+–Fe5+. 相似文献
14.
NANOPERM-type FeMoCuB alloys are studied using magnetic and Mössbauer measurements in the as-prepared amorphous state. It is shown that the Fe76Mo8Cu1B15 (A) and Fe74Mo8Cu1B17 (B) alloys exhibit the magnetic dipole and electrical quadrupole interactions well detected in the room-temperature Mössbauer spectra. The thermomagnetic measurements above the room temperature indicate a vanishing of the magnetic interactions at approximately 310 K (A) and at 340 K (B), respectively. The low-temperature DC magnetic measurements show an anomaly around 200 K which is also a boundary at which zero-field Mössbauer measurements of both samples reflect the gradual “vanishing” of the electrical quadrupole interactions and appearance of another magnetically ordered component. The Mössbauer measurements in the field of 4 MA/m yield a survival of quadrupole and an enhancement of magnetic dipole interactions. 相似文献
15.
Monica Sorescu Tianhong XuSteven Herchko 《Journal of magnetism and magnetic materials》2011,323(22):2859-2865
Differential scanning calorimetry, X-ray diffraction and room temperature Mössbauer spectrum measurements of Fe73.5Cu1Nb3Si13.5B9 (Finemet) alloy have been carried out in order to study its structural and magnetic properties as a function of annealing temperature. The DSC profile of as-quenched Finemet showed two exothermic peaks at 530 and 702 °C, corresponding to two crystallization processes. The Finemet alloy remains amorphous at 450 °C with one broad peak in XRD pattern and one broad sextet in Mössbauer spectrum. When the Finemet alloy was annealed at 550 °C, only well indexed body-center-cubic phase was detected. After being annealed at 650 and 750 °C, the XRD patterns showed the coexistence of α-Fe(Si) and Fe-B intermetallic phases with the increase in XRD peak intensities, indicating the growth of crystallites and the decomposition of Fe73.5Cu1Nb3Si13.5B9 alloy at elevated temperatures. The Mössbauer spectra of annealed Finemet alloy could be fitted with 4 or 5 sextets and one doublet at higher annealing temperatures, revealing the appearance of different crystalline phases corresponding to the different Fe sites above the crystallization temperature. The appearance of the nanocrystalline phases at different annealing temperatures was further confirmed by the recoilless fraction measurements. 相似文献
16.
Spectral studies of Co substituted Ni-Zn ferrites 总被引:1,自引:0,他引:1
M.A. Amer A. TawfikA.G. Mostafa A.F. El-ShoraS.M. Zaki 《Journal of magnetism and magnetic materials》2011,323(11):1445-1452
The spinel ferrites Zn0.35Ni0.65−xCoxFe2O4, 0≤x≤1, have been prepared using the standard ceramic technique. Room temperature Mössbauer, X-ray and infrared IR spectra were used for carrying out this study. X-ray patterns reveal that all the samples have single-phase cubic spinel structure. The Mössbauer spectra of the samples show a paramagnetic phase for x=0 and a six-line magnetic pattern and a central paramagnetic phase for x≥0.1. They are analyzed and attributed to two magnetic subpatterns and two quadrupole doublets due to Fe3+ ions at the tetrahedral A-sites and octahedral B-sites. Four absorption bands are observed in IR spectra. They confirm the spinel structure of the samples and existence of Fe3+ ions in the sample sublattices. The deduced hyperfine interactions, lattice parameters, absorption band positions and intensities and force constant are found to be dependent on the substitution factor x, where the cation distribution is estimated. The hyperfine magnetic fields, magnetization and lattice resonant frequency are found to be dependent on the interionic distance. 相似文献
17.
Nanocrystalline Fe particles were successfully prepared by the mechanical milling process using a high-energy planetary ball mill. The physical properties of the samples were investigated as a function of the milling time, t (in the 0-54 h range) by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and Mössbauer spectroscopy. After 54 h of milling, the lattice parameter increases from 0.28620 (3) nm for the starting Fe powder to 0.28667 (3) nm, the grain size decreases from 110 to 13 nm, while the strain increases from 0.09% to 0.7%. The powder particle morphology was observed by SEM at different stages of milling. For t less than 24 h, the Mössbauer spectra are characterized by one sextet corresponding to the crystalline bcc Fe phase, while for t greater than 24 h, the iron particles exhibit a two-component Mössbauer spectrum due to the presence of two phases: the crystallites bcc Fe phase and the grain-boundary region. The appearance and the increase in intensity of the second sextet with t may indicate that the interfacial region effect increases with milling time due to the grain size reduction and a probable disordered state of the grain boundaries. 相似文献
18.
The Cr-substituted M-type barium hexaferrites, BaFe12−xCrxO19, with x=0.0–0.8 have been successfully prepared by nitrate–citrate auto-combustion process using citric acid as a fuel/reductant and nitrates as oxidants. The resulting precursors were calcined at 1100 °C for 1 h and followed by sintering at 1200 °C for 12 h in oxygen atmosphere. The ferrites were systematically investigated by using powder X-ray diffractometer (XRD), magnetic hysteresis recorder, Mössbauer spectrometer, and scanning electron microscope (SEM). The XRD data show the formation of pure magnetoplumbite phase without any other impurity phases. Both a and c lattice parameters calculated by the Rietveld method systematically decrease with increasing Cr content. The effects of Cr3+ ions on the barium ferrites were reported and discussed in detail. The site preference of Cr3+ and magnetic properties of the ferrites have been studied using Mössbauer spectra and hystereses. The results show that the magnetic properties are closely related to the distributions of Cr3+ ions on the five crystallographic sites. The saturation magnetization systematically decreases, however, the coercivity increases with Cr concentration. The magnetization and Mössbauer results indicate that the Cr3+ ions preferentially occupy the 2a, 12k, and 4fVI sites. The average size of hexagonal platelets obtained by SEM photographs tends to decrease with respect to Cr content. 相似文献
19.
Lijun Zhao Hua Yang Lianxiang Yu Yuming Cui Xuepping Zhao Shouhua Feng 《Journal of magnetism and magnetic materials》2006
The effects of rare-earth ions with different radii and magnetic moments on the magnetic properties of Ni–Mn ferrite are investigated. X-ray diffraction pattern has shown the presence of cubic structure of spinel ferrite for all samples. The values of Ms and Hc are decreasing with increasing of testing temperatures for all samples. The Hc value of Ni0.7Mn0.3La0.1Fe1.9O4 reaches 1082 Oe at 2 K. Mössbauer spectra tested at 273 K indicate the presence of superparamagnetism for samples calcined at 873 K. 相似文献
20.
Sven-Ulf Weber Thorsten M. Gesing Götz Eckold Reinhard X. Fischer Fred-Jochen Litterst Klaus-Dieter Becker 《Journal of Physics and Chemistry of Solids》2014
The Bi2(FexGa1−x)4O9 oxide solid solution possessing a mullite-type structure has been investigated by 57Fe Mössbauer spectroscopy in dependence of composition (0.1≤x≤1) and temperature (293≤T/K≤1073). The spectra have been fitted with two doublets for tetrahedrally and octahedrally coordinated high-spin Fe3+ ions, respectively. The experimental areas of the subspectra were used to determine the distribution of iron on the two inequivalent structural sites. The fraction of iron cations occupying the octahedral site is found to increase with decreasing Fe content and the cation distribution is almost independent of temperature. The unusual temperature dependence of the quadrupolar splitting, QS, observed for the octahedral site with dQS/dT>0 is discussed in connexion with structural data for Bi2Fe4O9. The temperature dependence of Mössbauer isomer shifts and signal intensities is examined in the context of local vibrational properties of iron on the two inequivalent sites of the mullite-type lattice structure. 相似文献