共查询到20条相似文献,搜索用时 15 毫秒
1.
Ashok B. NawaleNilesh S. Kanhe K.R. PatilS.V. Bhoraskar V.L. Mathe A.K. Das 《Journal of Alloys and Compounds》2011,509(12):4404-4413
A rapid synthesis method is reported for magnetic nanoparticles of nickel ferrite involving thermal plasma assisted vapor phase condensation process. The as-synthesized samples were characterized by X-ray Diffraction, Transmission Electron Microscopy, Vibrating Sample Magnetometer and X-ray Photoelectron Spectroscopy techniques. The average particle size was determined from the TEM micrographs and found to be around 30 nm. The effects of reactor parameters on the magnetic and structural properties have been evaluated, to find the optimized parameters so as to achieve the highest values of saturation magnetization and coercivity. Reasonably high saturation magnetization (48 emu/g) has been assigned to the high degree of crystallinity, achieved on account of high temperature during the growth, and the cation redistribution. The high value of coercivity (115 Oe) is explained on the basis of possible lattice defects arising from the cation redistribution. Detailed analysis of cation distribution using the XRD line intensity data leads to the conclusion that these samples are iron deficit and nickel rich. 相似文献
2.
The structure and magnetic properties of Ce3−xGdxCo11B4 borides have been studied by X-ray powder diffraction (XRPD), magnetization and differential scanning calorimetry (DSC) measurements. X-ray analysis reveals that the compounds crystallize in the hexagonal Ce3Co11B4-type structure with P6/mmm space group. The substitution of Gd for Ce leads to an increase of the unit-cell parameter a and the unit-cell volume V, while the unit-cell parameter c decreases linearly. Magnetic measurements indicate that all samples are ordered magnetically below the Curie temperature. The Curie temperatures increase as Ce is substituted by Gd. The saturation magnetization at 4 K decreases upon the Gd substitution up to x = 1, and then increases. 相似文献
3.
Abdülhadi Baykal Nermin Kasapolu Yüksel Kseolu Muhammet S. Toprak Harun Bayrakdar 《Journal of Alloys and Compounds》2008,464(1-2):514-518
A simple hydrothermal route is demonstrated for the synthesis of nickel ferrite nanocrystals, NiFe2O4, using cetyltrimethylammonium bromide (CTAB) as the surfactant and NH3 and NaOH as hydrolyzing agents. Synthesized materials have been characterized by XRD, FTIR, ESR, and TEM techniques. It was found that crystallization in both hydrolyzing agent led to nanometric in size. Average particle size of prepared samples was calculated from TEM micrographs and varied significantly between samples prepared using different hydrolyzing agents; it was 12 nm when conc. NH3 was used and 50 nm when 2 M NaOH was used. Crystallite size obtained using Scherrer equation agreed well with the TEM observations with the respective values of 15 and 55 nm. ESR analysis showed single broad bands which might indicate the phase homogeneity of the materials. Furthermore, linewidths were observed to differ due to the difference in magnetization that depends on the particle size; NiFe2O4 sample hydrolysed with NH3 has a larger linewidth revealing its smaller particle size as confirmed by XRD and TEM techniques. 相似文献
4.
Copper spin dynamics in (Er0.5Y0.5)2Cu2O5 solid solution has been investigated by electron paramagnetic resonance (EPR) technique. The temperature dependence of the EPR integrated intensity of the resonance line has showed a pronounced maximum at low temperatures and has vanished at the transition to the antiferromagnetic ordering at TN = 11 K. The temperature at which the EPR integrated intensity reaches maximum was different for the heating and cooling runs. Study of the product of integrated intensity and temperature has allowed determination of the dominating interactions in a particular temperature range. A model used previously to describe the AFM modes in the antiferromagnetic state of Y2Cu2O5 was applied to explain the observed changes in the EPR spectra. A dimensional crossover from 2D to 3D magnetic behaviour was observed at 55 K and interpreted in terms of the spin correlation length. 相似文献
5.
H. R. Salva A. A. Ghilarducci R. D. Snchez C. Vzquez 《Journal of Alloys and Compounds》2000,310(1-2):44-46
We have measured the magnetic field dependence of the anelastic modulus and the electric resistance of a ceramic sample of the magnetoresistant perovskite La2/3Ca1/3MnO3 around the metal–insulator transition by the vibrating reed technique (2.5 KHz). Previous work [1] showed that the modulus becomes higher while the internal friction has a peak at the transition temperature (Tc=262 K). In this work, improvements made on the equipment allowed us to measure at constant deformations (<10−5) and magnetic fields up to 4500 Gauss. We made isothermal measurements of internal friction, modulus and resistance as a function of an applied magnetic field. We found that most of the changes induced by the magnetic field take place in a few degrees (almost 5 K) near the transition temperature where the changes in resistance are more important. Up to the highest magnetic field applied, we found 3% maximum variations of the modulus and no hysteresis while cycling the magnetic field. We suppose that the experiment is placed in the linear response of the inverse Wiedemann effect [2], due to the small deformations used, and that the ferromagnetic domain structure is responsible for the observed effects. Some additional measurements are needed (magnetic hysteresis loops) to be compared with our results. 相似文献
6.
L. Srinivasa Rao M. Srinivasa Reddy M. Rami Reddy N. Veeraiah 《Journal of Alloys and Compounds》2008,464(1-2):472-482
Li2O–MoO3–B2O3 glasses containing different amounts of V2O5, ranging from 0 to 1.5 mol%, were prepared. The dielectric properties (viz., constant ′, loss tan δ, AC conductivity σac over a wide range of frequency and temperature) have been studied as a function of the concentration of vanadium ions. The variation of AC conductivity with the concentration of V2O5 passes through a maximum at 0.8 mol% V2O5. In the high-temperature region, the AC conduction seems to be connected with the mixed conduction, viz., electronic and ionic conduction. The dielectric relaxation effects exhibited by these glasses have been analyzed quantitatively by pseudo Cole–Cole plot method and the spreading of relaxation times has been established. Further analysis of these results has been carried out with the aid of the data on ESR, IR and optical absorption spectra. 相似文献
7.
Complex oxides Ln2Mn2/3Re4/3O7 (Ln = Y, Er) and Y2Zn2/3Re4/3O7 with a zirkelite structure and hexagonal unit cells (space group P3121, z = 6) have been obtained. Static and dynamic magnetic susceptibility measurements show that these oxides possess spin-glass behavior at low temperatures. Valence combinations of d-metals in the oxides are Mn2+(Zn2+)–Re5+. It is supposed that the examined specimens Ln2Mn2/3Re4/3O7 (Ln = Y, Er) contain the second magnetic phase of an unknown composition. 相似文献
8.
Jianhui ShiDeming Liu Lizhu TongXuwei Yang Hua Yang 《Journal of Alloys and Compounds》2011,509(42):10211-10216
In this paper, we report on the bifunctional Fe3O4@SiO2@YP0.1V0.9O4:Dy3+ nanocomposites were prepared by the solvothermal method and sol-gel method. The structure, photoluminescence (PL) and magnetic properties of the nanocomposites were characterized by means of X-ray diffraction, scanning electron microscope, transmission electron microscope, PL excitation and emission spectra and vibration sample magnetometry. It is shown that Fe3O4@SiO2@YP0.1V0.9O4:Dy3+ nanocomposites with a core-shell structure present excellent fluorescent and magnetic properties. Additionally, the effects of the magnetic field on the luminescence properties of nanocomposites were discussed. 相似文献
9.
The Ce2Fe17−xMnx (x = 0-2) compounds demonstrate a complex temperature dependence of the magnetocaloric effect MCE, which is inverse in a narrow temperature interval just below Néel temperature TN and normal at higher or lower temperatures. The normal MCE exhibits two peaks in the vicinity of temperatures of ferromagnetic ordering ΘT and TN for compositions x = 0-0.35, 1.3-2 or one peak near TN for antiferromagnets with x = 0.5-1. The maximal change of the peak entropy −SM is about 3 J/kg K in a field of 5 T for the compounds with x = 0-0.5 at T ∼230 K close to TN. The drastic decrease of the MCE, by half, in the Ce2Fe17−xMnx system is traceable to a decrease of the spontaneous magnetization and the helical type of magnetic states in the compounds. 相似文献
10.
X.L. Li H.A. Ma Y.J. Zheng Y. Liu G.H. Zuo W.Q. Liu J.G. Li X. Jia 《Journal of Alloys and Compounds》2008,463(1-2):412-416
The magnetic and dielectric properties of Bi–Zn codoped Y-type hexagonal ferrite was investigated. The samples with composition of Ba2−xBixZn0.8+xCo0.8Cu0.4Fe12−xO22 (x = 0–0.4) were prepared by the solid-state reaction method. Phase formation was characterized by X-ray diffraction. The microstructure was observed via scanning electron microscopy. The magnetic and dielectric properties were measured using an impedance analyzer. Direct current (dc) electrical resistivity was measured using a pA meter/dc voltage source. Minor Bi doping (x = 0.05–0.25) will not destroy the phase formation of Y-type hexagonal ferrite, but lower the phase formation temperature distinctly. Bi substitution can also promote the sintering process. The Bi-containing samples (x > 0.05) can be sintered well under 900 °C without any other addition. The sintering temperature is about 200 °C lower than that of the Bi-free sample. The Bi–Zn codoped samples exhibit excellent magnetic and dielectric properties in hyper frequency. These materials are suitable for multi-layer chip-inductive components. 相似文献
11.
T. PrabhakaranJ. Hemalatha 《Journal of Alloys and Compounds》2011,509(25):7071-7077
A combustion route of synthesizing highly crystalline single phase nickel ferrite (NiFe2O4) spinel nanoparticles using various amounts of dl-alanine as fuel has been reported in this paper. The role of the amount of fuel is found to be significant in the size control and phase purity of nano crystalline samples. The structural, thermal, morphological and magnetic studies have been carried out. XRD patterns reveal the formation of highly crystalline nano NiFe2O4 with high degree of phase purity when fuel concentration is maintained at 1 M and 2 M. FTIR spectra also prove the formation of pure nano NiFe2O4. The temperature and fuel effects are found to have strong influence on size, structural, and magnetic properties of materials. The magnetic measurements show that the nano NiFe2O4 samples exhibit soft ferromagnetism with the highest saturation magnetization Ms at room temperature as 42.53 emu/g. 相似文献
12.
Electron magnetic resonance (EMR) spectra of gadolinium-doped lanthanum oxide powders have been studied at room-temperature for Gd concentrations between 0.02 and 2.00 mol.%. The results suggest that Gd3+ ions occupy substitutional sites, that the EMR linewidth and intensity increase with increasing Gd concentration and that the range of the exchange interaction between Gd3+ ions is about 0.39 nm, much smaller than that of the same ion in other rare earth oxide. 相似文献
13.
Chunjiang LengJianhong Wei Zhengyou LiuJing Shi 《Journal of Alloys and Compounds》2011,509(6):3052-3056
Using cobalt ferrite (CoFe2O4) nanoparticles of different content as nucleation sites, polyaniline-CoFe2O4 nanofiber composites were successfully synthesized at the interface of water and ionic liquid via in-situ polymerization. Structure and morphology were investigated by TGA, TEM, XRD, and FT-IR. The influence of ionic liquids on the structure, conductivity and magnetic property of polyaniline-CoFe2O4 nanocomposites were studied in detail. The results show that imidazolium-based ionic liquids BMIPF6 acts as an anchor agent during the nanofiber composites formation process. Introduction of ionic liquids obviously improves the conductivity but weakens the magnetization of polyaniline-CoFe2O4 nanocomposites in the same [CoFe2O4]/[An] ratio. 相似文献
14.
S. Bala Murali KrishnaD. Krishna Rao 《Journal of Alloys and Compounds》2011,509(27):7373-7380
Five glasses in the quaternary system 5 ZnO-(50 − x) As2O3-45 Sb2O3: x WO3 with the values of x ranging from 0 to 20 mol% (in steps of 5 mol%) are prepared. The samples are characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy (EDS) and differential thermal analysis (DTA) techniques. The DTA studies have indicated that the glass forming ability decreases with the increasing content of WO3. A number of studies, like, spectroscopic (optical absorption, IR, Raman, ESR spectra) and dielectric studies (dielectric constant ?, loss tan δ, a.c. conductivity σa.c.) over a wide range of frequency and temperature and dielectric break down strength at room temperature, have been carried out and are analysed in the light of different oxidation states and environment of tungsten ions in these glasses. These glasses have potential photonic applications. 相似文献
15.
T.F. Marinca I. Chicina? O. IsnardV. Pop F. Popa 《Journal of Alloys and Compounds》2011,509(30):7931-7936
Nanocrystalline nickel ferrite (NiFe2O4) has been synthesized from a stoichiometric mixture of oxides NiO and α-Fe2O3 in a high energy planetary mill. An annealing at 350 °C, after milling, was used to improve the solid state reaction. The obtained powders were investigated by X-ray diffraction, magnetic measurements, scanning electron microscopy, X-ray microanalysis and differential scanning calorimetry. The particles size distribution was analyzed using a laser particle size analyser. The nickel ferrite begins to form after 4 h of milling and continuously form up to 16 h of milling. The obtained nickel ferrite has many inhomogeneities and a distorted spinel structure. The mean crystallites size at the final time of milling is 9 ± 2 nm and the lattice parameter increases with increase the milling time. DSC measurements revealed a large exothermic peak associated with cations reordering in the crystalline structure. The magnetization of the obtained powder depends on the milling time and annealing. After the complete reaction between the starting oxides the milling reduces the magnetization of the samples. The magnetization increases after annealing, due to the reorganization of the cations into the spinel structure. 相似文献
16.
The HfFe6Ge6-type RMn6Sn6−xXx′ solid solutions (R=Tb, Dy, X′=Ga, In; x≤1.4) have been studied by powder magnetization measurements. All the series are characterized by ferrimagnetic ordering and by a decrease in Curie temperatures with the substitution (ΔTc/Δx≈−39 K for X′=Ga and ΔTc/Δx≈−75 K for X′=In). The RMn6Sn6−xGax systems are characterized by a strong decrease in the spin reorientation temperature with substitution (ΔTt/Δx≈−191 K and −78 K for R=Tb and Dy, respectively) while this transition almost does not change in systems containing indium. The coercive fields drastically decrease with the substitution in the TbMn6Sn6−xGax system while the substitution of In for Sn has a weaker effect. The coercive fields of the Dy compounds do not vary greatly with the substitution in both series. The behaviour of the TbMn6Sn6−xGax is compared with the evolutions observed in the TmMn6Sn6−xGax series. This comparison strongly suggests that the replacement of Sn by Ga changes the sign of the A02 crystal field parameter. 相似文献
17.
A.V. Morozkin O. Isnard P. Henry P. Manfrinetti R. Nirmala S.K. Malik 《Journal of Alloys and Compounds》2008,450(1-2):62-74
Investigations were made by neutron diffraction on Zr6CoAs2-type (space group no. 189) Ho6−xErxMnBi2 solid solutions. The ferromagnetic ordering temperature decreases from Ho6MnBi2 (TC = 200(6) K) to Er6MnBi2 (TC = 100(4) K), whereas temperatures of ferrimagnetic (or antiferrimagnetic) ordering (TFerri and TAFerri) are found to have non-monotonic dependences on the content of Er: TFerri = 58(4) K for Ho6MnBi2, TFerri = 162(4) K for Ho4.5Er1.5MnBi2, TFerri = 150(4) K for Ho3Er3MnBi2, TAFerri = 78(4) K for Ho1.5Er4.5MnBi2 and TAFerri = 52(4) K for Er6MnBi2.
In these compounds, no local moment was detected on the manganese ion site, except for Ho1.5Er4.5MnBi2 and Er6MnBi2 compounds. The manganese magnetic moments (μMn) is 1.5μB and these are antiferromagnetically coupled with that of rare earth moments. 相似文献
18.
P.A. Shaikh R.C. Kambale A.V. Rao Y.D. Kolekar 《Journal of Alloys and Compounds》2009,482(1-2):276-282
Nickel-doped iron-deficient cobalt ferrite with small amount of manganese having the chemical composition Co1−xNixFe1.9Mn0.1O4, with x = 0.2, 0.4, 0.6 and 0.8, were prepared by standard double sintering ceramic method. The spinel phase formation was confirmed by X-ray diffraction (XRD). The DC resistivity measurements with temperature indicate a semiconducting behavior showing a linear decrease with increasing temperature and the doping of Ni enhances the resistivity. Maximum resistivity of the order of 109 Ω cm was found for composition x = 0.8. Room temperature dielectric constant measurements with frequency (100 Hz to 1 MHz), show usual dielectric dispersion. Also, the variation of room temperature AC conductivity as a function of frequency were studied and explained by using Maxwell–Wagner two-layer model. The studies on dielectric constant (′), loss tangent (tan δ) and AC conductivity (σAC), at four different frequencies (viz., 1, 10, 100 kHz and 1 MHz), with temperature were made. 相似文献
19.
In this study we give evidence for the strong dependence of the compositional and magnetic properties on the synthesis conditions of polycrystalline Co2(Cr1−xFex)Al Heusler alloys (0 ≤ x ≤ 1) by comparing the properties of as-grown and annealed compounds. Strong chemical inhomogeneities are found at the micrometric level depending on the compound and the synthesis method. Moreover, we find that the Co content is homogeneous at the micrometric level in all the studied samples in sharp contrast with significant inhomogeneous distribution of (Fe/Cr) and Al at the micrometric level, especially for Cr-rich compounds (x ≤ 0.4). We have found that the magnetic properties (the Curie temperature and the saturation magnetization) are strongly depressed in the annealed compounds with respect to the corresponding as-grown compounds. For the as-grown compounds the saturation magnetization is close to the theoretically predicted one for x ≥ 0.7 whereas it is lower than the theoretically predicted one for x ≤ 0.4, which correlates with the observed chemical inhomogeneity. 相似文献
20.
《Journal of Alloys and Compounds》2004,370(1-2):47-52
The structure and magnetic properties of the Pr1−xGdxMn2Ge2 (0.0≤x≤1.0) compounds have been investigated by means of X-ray diffraction (XRD), differential scanning calorimetry (DSC) techniques and AC magnetic susceptibility measurements. All compounds crystallize in the ThCr2Si2-type structure with the space group I4/mmm. The lattice constants and the unit cell volume obey Vegard’s law. Samples in this alloy system exhibit a crossover from ferromagnetic ordering for PrMn2Ge2 to antiferromagnetic ordering for GdMn2Ge2 as a function of Gd concentration x. At low temperatures, the rare earth sublattice also orders and reconfigures the ordering in the Mn sublattice. The results are summarized in the x–T magnetic phase diagram. 相似文献