共查询到17条相似文献,搜索用时 10 毫秒
1.
J. GondroJ. ?wierczek J. OlszewskiJ. Zbroszczyk K. SobczykW.H. Ciurzyńska J. Rz?ckiM. Nabia?ek 《Journal of magnetism and magnetic materials》2012,324(7):1360-1364
Microstructure by X-ray diffraction and Mössbauer spectroscopy, and isothermal magnetic entropy changes in the bulk amorphous Fe60Co5Zr8Mo5W2B20 alloy in the as-quenched state and after annealing at 720 K for 15 min are studied. The as-cast and heat treated alloy is paramagnetic at room temperature. The quadrupole splitting distribution is unimodal after annealing indicating the more homogenous structure in comparison with that for the as-cast alloy. Curie temperature slightly increases after annealing from 265±2 K in the as-quenched state to 272±2 K and the alloy exhibits the second order magnetic phase transition. The maximum of isothermal magnetic entropy changes appears at the Curie points and is equal to 0.30 and 0.42 J/(kg·K) for the alloy in the as-quenched state and after annealing, respectively. In the paramagnetic region the material behaves as a Curie-Weiss paramagnet. 相似文献
2.
A. Grabias M. Kopcewicz J. Latuch M. P?ka?a 《Journal of magnetism and magnetic materials》2010,322(20):3137-3141
Structural and magnetic properties of two rapidly solidified and post-annealed Fe60Pt15B25 and Fe60Pt25B15 alloys are compared. The as-quenched Fe60Pt15B25 ribbon was fully amorphous whereas in the Fe60Pt25B15 alloy the amorphous phase coexists with an fcc FePt disordered solid solution. Differential scanning calorimetry curves of both alloys reveal a single exothermal peak with onset temperatures of 873 and 847 K for Fe60Pt15B25 and Fe60Pt25B15, respectively. Magnetically hard, tetragonal ordered L10 FePt and magnetically soft Fe2B nanocrystalline phases were formed due to the annealing of the alloys, as indicated by X-ray diffraction and Mössbauer spectroscopy measurements. Two-phase behavior was detected in the temperature dependence of magnetization of the annealed samples. A magnetic hardening was observed for all annealed ribbons. Magnetic properties of the annealed alloys, studied by hysteresis loop measurements, were related to the differences in the relative fractions of the hard and soft magnetic phases calculated from Mössbauer spectra. The alloy with 25 at% Pt exhibits better hard magnetic properties (Hc=437 kA/m, Mr/Ms=0.74) than the alloy with smaller Pt content (Hc=270 kA/m, Mr/Ms=0.73) mainly due to the larger abundance of the ordered tetragonal FePt phase. 相似文献
3.
J. ?wierczek 《Journal of magnetism and magnetic materials》2010,322(18):2696-9345
High-resolution electron microscopy (HREM) reveals in the as-quenched Fe90Zr7B3 alloy the existence of medium range ordered (MRO) regions 1-2 nm in size. Transmission Mössbauer spectroscopy confirms that these regions are α-Fe MRO ones. Above the Curie point of the amorphous phase (TC=(257±2)K) they behave like non-interacting superparamagnetic particles with the magnetization decreasing linearly with the temperature. For these particles the average magnetic moment of 390μB and the average size of 1.7 nm, in excellent agreement with HREM observations, were estimated. The maximum of the isothermal magnetic entropy change at the maximum magnetizing field induction of 2 T occurs at the Curie temperature of the amorphous phase and equals to 1.05 Jkg−1 K−1. The magnetic entropy changes exhibit the linear dependence on the maximum magnetizing field induction in the range 0.5-2 T below, near and above TC. Such correlations are attributed to superparamagnetic behavior of α-Fe MRO regions. 相似文献
4.
M.T. Sandor X.K. XiJ.Q. Wang H.Y. BaiW.H. Wang Y. Wu 《Journal of magnetism and magnetic materials》2012,324(2):173-177
We report magnetization properties of (CuZr)93−xAl7Gdx bulk metallic glasses from temperature dependent 27Al nuclear magnetic resonance spectroscopy and magnetic susceptibility measurements. Significant non-linear line broadening of 27Al spectra commencing at high temperatures is attributed to the development of a local magnetic susceptibility distribution that prevails over a finite temperature range. Magnetization measurements confirm the linewidth enhancement due to strong frustrated magnetic short-range order. This study provides insight into the nature of magnetic development and frustration in paramagnetic systems. 相似文献
5.
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
6.
The infrared (IR) and 57Fe-Mössbauer spectra of Fe3IIFe4III(AsO4)6 were recorded and analyzed on the basis of its structural characteristics. The IR spectrum presents a high complexity, showing an important number of bands and splittings, as a consequence of the presence of three structurally independent AsO43− groups. The analysis of the four quadrupole signals shown by the Mössbauer spectrum allowed to attain a detailed insight into the cation distribution over the available crystallographic sites. The alternating current susceptibility measurements indicate a paramagnetic to ferrimagnetic transition in the material at about 59 K. 相似文献
7.
Monica Sorescu Tianhong XuAdam Wise Marina Díaz-MichelenaMichael E. McHenry 《Journal of magnetism and magnetic materials》2012,324(7):1453-1462
The xFe2TiO4-(1−x)Fe3O4 pseudo-binary systems (0≤x≤1) of ulvöspinel component were synthesized by solid-state reaction between ulvöspinel Fe2TiO4 precursors and commercial Fe3O4 powders in stochiometric proportions. Crystalline structures were determined by X-ray powder diffraction (XRD) and it was found that the as-obtained titanomagnetites maintain an inverse spinel structure. The lattice parameter a of synthesized titanomagnetite increases linearly with the increase in the ulvöspinel component. 57Fe room temperature Mössbauer spectra were employed to evaluate the magnetic properties and cation distribution. The hyperfine magnetic field is observed to decrease with increasing Fe2TiO4 component. The fraction of Fe2+ in both tetrahedral and octahedral sites increases with the increase in Ti4+ content, due to the substitution and reduction of Fe3+ by Ti4+ that maintains the charge balance in the spinel structure. For x in the range of 0 ≤x≤0.4, the solid solution is ferrimagnetic at room temperature. However, it shows weak ferrimagnetic and paramagnetic behavior for x in the range of 0.4<x≤0.7. When x>0.70, it only shows paramagnetic behavior, with the appearance of quadrupole doublets in the Mössbauer spectra. Simultaneous differential scanning calorimetry and thermogravimetric analysis (DSC-TGA) studies showed that magnetite is not stable, and thermal decomposition of magnetite occurs with weight losses accompanying with exothermic processes under heat treatment in inert atmosphere. 相似文献
8.
C.L. Zhang J. ChenT.Z. Wang G.X. XieC. Zhu D.H. Wang 《Physica B: Condensed Matter》2011,406(14):2840-2842
The first-order phase transitions in NdFe12B6 and PrFe12B6 alloys give rise to giant values of magnetic entropy changes in relatively low field. However, the metastable nature of these alloys associates with a special procedure of preparation and considerable amount of impurities inevitably. By alloying NdFe12B6 with the iso-structural compound of NdCo12B6 appropriately, a Nd(Co1−xFex)12B6 system which possesses the stable SrNi12B6-type structure can be obtained directly via the standard casting-and-annealing method. Remarkably improved thermal and magnetic reversibility are observed in the present system. The second-order phase transitions in NdCo12B6 alloy give rise to the relative cooling power, which is comparable with that of NdFe12B6 alloy around the ordering temperature. 相似文献
9.
Xiaoping Zheng Fashen Li Baogen Shen 《Journal of magnetism and magnetic materials》2009,321(23):3842-3846
The effect of Pr substitution for Dy on the magnetization, magnetostriction, anisotropy and spin reorientation of a series of Tb0.3Dy0.7−xPrx(Fe0.9Al0.1)1.95 alloys (x=0, 0.1, 0.20, 0.25, 0.30, 0.35) at room temperature has been investigated. It was found that the magnetization and magnetostriction of the homogenized Tb0.3Dy0.7−xPrx(Fe0.9Al0.1)1.95 alloys decreases drastically with increasing x and the magnetostrictive effect disappears for x>0.2, but the spontaneous magnetostriction λ111 increases approximately linearly with increasing x. Moreover, the magnetostriction exhibits slightly bigger value at x=0.1 than the free alloys and is saturated more easily with the magnetic field H, showing that a small amount of Pr substitution is beneficial to a decrease in the magnetocrystalline anisotropy. The analysis of the Mössbauer spectra indicated that the easy magnetization direction in the {1 1 0} plane deviates slightly from the main axis of symmetry with Pr concentration x, namely spin reorientation. Comparing with the Al substitution, the effect of Pr substitution for Dy on the spin reorientation is smaller. 相似文献
10.
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
11.
Amorphous-crystalline dual-layer structures resulting from metastable liquid phase separation in (Fe50Co25B15Si10)80Cu20 melt-spun ribbons
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(Fe50Co25B15Si10)80Cu20 ribbons are prepared by using the single-roller melt-spinning method. A dual-layer structure consisting of a (Fe, Co)-rich amorphous phase and a Cu-rich crystalline phase forms due to metastable liquid phase separation before solidification. The magnetic hysteresis loops of the as-quenched and annealed samples are measured at room temperature. It is indicated that the coercivity of the ribbon is almost zero in the as-quenched state. The crystallization leads to the increase of coercivity and decrease of saturation magnetization. 相似文献
12.
Monica Sorescu L. Diamandescu D. Tarabasanu-Mihaila B.H. Howard 《Journal of Physics and Chemistry of Solids》2004,65(5):1021-1029
Structural and morphological characteristics of (1−x)α-Fe2O3-xSnO2 (x=0.0-1.0) nanoparticles obtained under hydrothermal conditions have been investigated by X-ray diffraction (XRD), transmission Mössbauer spectroscopy, scanning and transmission electron microscopy as well as energy dispersive X-ray analysis. On the basis of the Rietveld structure refinements of the XRD spectra at low tin concentrations, it was found that Sn4+ ions partially substitute for Fe3+ at the octahedral sites and also occupy the interstitial octahedral sites which are vacant in α-Fe2O3 corundum structure. A phase separation of α-Fe2O3 and SnO2 was observed for x≥0.4: the α-Fe2O3 structure containing tin decreases simultaneously with the increase of the SnO2 phase containing substitutional iron ions. The mean particle dimension decreases from 70 to 6 nm, as the molar fraction x increases up to x=1.0. The estimated solubility limits in the nanoparticle system (1−x)α-Fe2O3-xSnO2 synthesized under hydrothermal conditions are: x≤0.2 for Sn4+ in α-Fe2O3 and x≥0.7 for Fe3+ in SnO2. 相似文献
13.
In this study, Cu and Nb content dependences of magnetic properties for annealed Fe84−x−yCuxNbySi4B12 alloy ribbons fabricated by melt spinning were investigated. In Fe83−xCuxNb1Si4B12 alloy systems, the coercivity Hc markedly decreases with increasing x and exhibits a minimum at around x=1.0-1.2, while the saturation magnetic flux density Bs shows a slight variation. In Fe83−yCu1NbySi4B12 alloy systems, Hc markedly decreases at around y=0.5, while Bs shows a monotonic decrease. Fe82Cu1Nb1Si4B12 nanocrystalline alloy ribbons exhibit a high Bs of 1.78 T and a low Hc of 3.2 A/m. The core losses of the present alloys at 1.0 T at 400 Hz, P10/400, and at 1.0 T at 1 kHz, P10/1k, are 1.3 and 4.4 W/kg, respectively. 相似文献
14.
FexNi100−x thin films were produced by galvanostatic electrodeposition on Si (1 0 0), nominal thickness 2800 nm, and x ranging 7-20. The crystalline structure of the sample was determined by X-ray diffraction (XRD). The magnetic properties were investigated by vibration sample magnetometry (VSM) and room temperature 57Fe Mössbauer spectroscopy. Conversion Electron Mössbauer spectroscopy (CEMS) in both film surfaces for the thick self-supported films showed that the magnetic moment direction is in the plane and conventional transmission (MS) that the directions are out of the plane films. The results were interpreted assuming a three-layer model where the external layer has in-plane magnetization and the internal one, out of plane magnetization. 相似文献
15.
对熔体急冷法制备的非晶合金 Fe52Co34Hf7B6Cu1 进行了不同频率的中频磁脉冲处理, 用透射电子显微镜、穆斯堡尔谱、正电子湮没寿命谱等方法研究了处 理前后试样的微观结构及结构缺陷变化. 结果表明,经中频磁脉冲处理后,样品发生了部分纳米晶化, 晶化量随磁脉冲频率增加而增加, 当磁脉冲频率为2000 Hz时, 晶化量达33.1%; 在淬态非晶样品中, 正电子在类单空位中的湮没寿命τ1为150.5 ps, 强度 I1为77.7%, 在微孔洞中的湮没寿命τ2为349.7 ps,强度I2为22.3%; 随磁脉冲频率的增加, τ1, τ2值呈现减小的变化趋势, 与淬态非晶相比, I1有所增加, I2下降, τ1, τ2的平均值τ大幅降低. 相似文献
16.
The structure and magnetostriction of the (Tb1−xDyx)0.2Pr0.8(Fe0.4Co0.6)1.88C0.05 intermetallic compounds (0≤x≤1) were studied by X-ray diffraction and magnetic measurements. The formation of an approximate single Laves phase with a MgCu2-type cubic structure was observed in this series of compounds. It was found that the Curie temperature and the saturation magnetization of the compounds would decrease with increase in the Dy content up to x=1. The magnetostriction λa (λa=λ‖-λ⊥) gently rises when x≤0.6, and follows with a precipitous fall when x exceeds 0.6, with the highest value of λa being reached in the compounds with x=0.6. The magnetostriction of all the samples was observed to approach their own saturation in the magnetic fields higher than 4 kOe. This indicates that the addition of a small amount of Dy could effectively improve the low-field magnetostriction of the Tb0.2Pr0.8(Fe0.4Co0.6)1.88C0.05 compounds, which could become a kind of promising magnetostrictive material. 相似文献
17.
Fangting Lin 《Journal of magnetism and magnetic materials》2010,322(14):2081-493
Fe-doped (Ba1−xSrx)TiO3 ceramics were prepared by solid-state reaction, and ferromagnetism was realized at room temperature. The microstructure and magnetism were modified by the Sr concentration control (0≤x≤75 at%) at a fixed Fe concentration, and the relevant magnetic exchange mechanism was discussed. All the samples are shown to have a single perovskite structure. When increasing the Sr concentration, the phase structure is transformed from a hexagonal perovskite into a cubic perovskite, with a monotonic decrease in lattice parameters induced by ionic size effect. The room-temperature ferromagnetism is expected to originate from the super-exchange interactions between Fe3+ on pentahedral and octahedral Ti sites mediated by the O2− ions. The increase in Sr addition modifies two main influencing factors in magnetic properties: the ratio of pentahedral to octahedral Fe3+ and the concentration of oxygen vacancies, leading to a gradually enhanced saturation magnetization. The highest value, obtained for Fe-doped (Ba0.25Sr0.75)TiO3, is an order of magnitude higher than that of the Fe-doped BaTiO3 system with similar Fe concentration and preparation conditions, which may indicate (Ba1−xSrx)TiO3 as a more suitable matrix material for multiferroic research. 相似文献