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1.
Co1−xZnxFe2O4 nanoparticles were prepared by co-precipitation method with x varying from 0 to 1.0. The powder samples were characterized by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR). The average crystallite sizes of the particles were determined from XRD. X-ray analysis showed that the samples were cubic spinel. The average crystallite size (DaveXR) of the particles precipitated was found to vary from 6.92 to 12.02 nm decreasing with the increase in zinc substitution. The lattice constant (ao) increased with the increase in zinc substitution. The specific saturation magnetization (MS) of the particles was measured at room temperature. The magnetic parameters such as MS, Hc, and Mr were found to decrease with the increase in zinc substitution. FTIR spectra of the Co1−xZnxFe2O4 with x varying from 0 to 1.0 in the range 400–4000 cm−1 were reported. The spinel structure and the crystalline water adsorption of Co1−xZnxFe2O4 nanoparticles were studied by using FTIR. 相似文献
2.
X.K. Lv W. LiuW.J. Ren B. LiX.G. Zhao D. LiZ.D. Zhang 《Journal of magnetism and magnetic materials》2008
The C15 Laves phases with composition Nd1−xPrx(Fe0.35Co0.55B0.1)2 (0?x?1) have been synthesized by arc melting and subsequent annealing. The Curie temperature Tc and the saturation magnetizations Ms at 5 and 295 K decrease with increasing Pr content. The linear anisotropic magnetostriction λa=λ∥−λ⊥ at room temperature for Nd1−xPrx(Fe0.35Co0.55B0.1)2 alloys with 0?x?0.4 initially reaches a negative minimum, then increases and changes its sign with increasing magnetic field H, and the λa for the alloys with x?0.6 is positive and increases as magnetic field H increases. 相似文献
3.
Ni1−xCoxFe2O4 (x=0.6, 0.8 and 0.9) nanoparticles have been synthesized with various crystallite sizes depending on the thermal treatments and composition (cobalt content) using the sol-gel combustion method. The size of nanoparticles has been controlled by thermal treatment. On the other hand, the magnetic property of the ferrite has been controlled by changing the heat treatment. Morphology and particle sizes of Ni1−xCoxFe2O4 have been studied using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The presence of functional group has been identified by Fourier Transform Infrared (FTIR) spectra. From TGA-DTA studies, the weight gains of Ni1−xCoxFe2O4 nanoparticles have been observed and it might be due to capping organic molecules with oxygen at temperatures above 200 °C. Magnetic properties of Ni1−xCoxFe2O4 particles have been analysed using VSM and it is found that saturation magnetization (Ms) has increased with particle size and has coercivity (Hc) increased initially and then decreased. The Ms and Hc values decreased with the increase of content of cobalt in Ni1−xCoxFe2O4. 相似文献
4.
Zan Yao 《Journal of magnetism and magnetic materials》2009,321(3):203-206
Phase structure and magnetic properties of the as-cast and as-milled/annealed SmCo7−xMox (x=0, 0.1, 0.2, 0.3, 0.4) alloys have been systematically studied. It is found that all the as-cast series alloys are composed of the CaCu5-type and Th2Zn17-type phases. Saturation magnetization of the samples decreases with the Mo content increasing. Intrinsic coercivities (iHc) of no more than 0.06 T are observed in these as-cast samples, due to their rather coarse grain microstructures with an average grain size of 50 μm. The as-milled/annealed SmCo7−xMox powders crystallize in the disordered TbCu7-type (1:7) structure with very fine nanograins, and a minor Co3Mo phase appears in the samples with x=0.1-0.4. High iHc (?0.95 T) are achieved in these samples, with a maximum of 1.26 T located at x=0.2, which can be primarily attributed to strong pinning of the domain wall motion at the nanograin boundaries. The temperature coefficient (β) of the iHc is about −0.22%/°C in the temperature range of 25-400 °C for the as-milled/annealed samples. 相似文献
5.
K. Kaabi 《Journal of Physics and Chemistry of Solids》2004,65(11):1759-1764
Chemical preparation, calorimetric studies, crystal structure and spectroscopic investigations are given for a new noncentrosymmetric organic cation monophosphate [2,5-(CH3)2C6H3NH3]H2PO4. This compound is orthorhombic P212121 with the following unit-cell parameters: a=5.872(4), b=20.984(3), c=8.465(1) Å, Z=4, V=1043.0(5) Å3 and Dx=1.396 g cm−3. Crystal structure has been solved and refined to R=0.048 using 2526 independent reflections. Structure can be described as an inorganic layer parallel to (a,b) planes between which organic groups [2,5-(CH3)2C6H3NH3]+ are located. Multiple hydrogen bonds connecting the different entities of compound thrust upon three-dimensional network a noncentrosymmetric configuration. 相似文献
6.
Superparamagnetic nanoparticles of the spinel ferrite four-element system Mn1−xZnx[Fe2−yLy]O4 (where L:Gd3+, La3+, Ce3+, Eu3+, Dy3+, Er3+,Yb3+) were synthesized by the co-precipitation method. The magnetic moments of the 10 nm diameter nanoparticles were comparable to the ones of Fe3O4 nanoparticles. A comparatively low TC (∼52–72 °C) was observed for some of the compositions. The heating mechanism of the superparamagnetic particles in the AC magnetic field at radiofrequency range is discussed and especially the absence of the hysteresis loop in the M–H curve at room temperature. One possible explanation—spontaneous particle agglomeration—was experimentally verified. 相似文献
7.
N.V. Khiem P.T. Phong D.N.H. Nam N.X. Phuc 《Journal of magnetism and magnetic materials》2009,321(13):2027-2031
The critical parameters provide important information concerning the interaction mechanisms near the paramagnetic-to-ferromagnetic transition. In this paper, we present a thorough study for the critical behavior of La0.7A0.3(Mn1−xBx)O3 (A=Sr; B=Ti and Al; x=0.0 and 0.05) polycrystalline samples near ferromagnetic-paramagnetic phase transition temperature by analyzing isothermal magnetization data. We have analyzed our dc-magnetization data near the transition temperature with the help of the modified Arrot plot, Kouvel-Fisher method. We have determined the critical temperature TC and the critical parameters β, γ and δ. With the values of TC, β and γ, we plot M×(1−T/TC)−β vs. H×(1−T/TC)−γ. All the data collapse on one of the two curves. This suggests that the data below and above TC obey scaling, following a single equation of state. Critical parameters for x=0 and xTi=0.05 samples are between those predicted for a 3D-Heisenberg model and mean-field theory and for xAl=0.05 samples the values obtained for the critical parameters are close to those predicted by the mean-field theory. 相似文献
8.
Luminescent properties of KGd1−x(WO4)2:Eux and KGd1−x(WO4)2−y(MoO4)y:Eux phosphors in UV-VUV regions
KGd1−x(WO4)2−y(MoO4)y:Eu3+x(0.1?x?0.75, y=0 and 0.2) phosphors are synthesized through traditional solid-state reaction and their luminescent properties in ultraviolet (UV) and vacuum ultraviolet (VUV) regions are investigated. Under 147 nm excitation, these phosphors show characteristic red emission with good color purity. In order to improve their emission intensity, the MoO42− (20 wt%) is introduced into the anion of KGd1−x(WO4):Eu3+x. The Mo6+ and Eu3+ co-doped KGd(WO4)2 phosphors show higher emission intensity in comparison with the singly Eu3+-doped KGd(WO4)2 in VUV region. The chromaticity coordination of KGd0.45(WO4):Eu3+0.55 is (x=0.669, y=0.331), while that of KGd0.45(WO4)1.8(MoO4)0.2:Eu3+0.55 is (x=0.666, y=0.334) in VUV region. 相似文献
9.
Jun Shen Yang-Xian Li Ji-Rong Sun 《Journal of magnetism and magnetic materials》2009,321(15):2336-2339
Magnetic entropy change ΔSm, hysteresis loss and refrigerant capacity of NaZn13-type La0.7Pr0.3Fe13−xSix (1.5?x?2.0) compounds have been investigated. The Curie temperature TC increases linearly with the increase of silicon concentration. Although the maximum value of ΔSm under a field change of 0−5 T decreases from 30.5 to 11.4 J/kg K as x increases from 1.5 to 2.0, the hysteresis loss at TC reduces remarkably from 89.2 J/kg for x=1.5 to zero for x=2.0 because the increase of Si content can weaken the itinerant electron metamagnetic transition. The effective refrigerant capacity RCeff is maintained at high values of 362−439 J/kg for a field change of 0−5 T. This implies that a large ΔSm and a high RCeff can be achieved simultaneously in the La0.7Pr0.3Fe13−xSix compounds. 相似文献
10.
J.Q. Li M. Ouyang F.S. Liu D.C. Liu W.Q. Ao 《Journal of magnetism and magnetic materials》2009,321(17):2541-2546
The TbFe6−xGa6+x compounds (x=0, 0.5, 1.0 and 1.45) have been prepared and studied by X-ray powder diffraction and magnetization measurements. The structure of the compound TbFe6−xGa6+x transfers from the orthorhombic ScFe6Ga6-type structure (space group Immm) (x=0 and 0.5) to the tetragonal ThMn12-type structure (space group I4/mmm) (x=1.0 and 1.5) and the volume of the unit cell increases as Ga content increases. The lattice parameters are a=0.85551, b=0.8626 and c=0.50717 nm for TbFe6Ga6, and a=0.86938 and c=0.50918 nm for TbFe4.55Ga7.45.The magnetization measurements indicate all the TbFe6−xGa6+x compounds have magnetic ordering. The Curie temperatures decrease from 492 K for TbFe6Ga6 to 327 K for TbFe4.55Ga7.45. The magnetization of the TbFe6−xGa6+x decreases with temperature decreases below its magnetic ordering temperature due to the increasing Tb-sublattice magnetization which is antiparallel to the Fe-sublattice magnetization. 相似文献
11.
H.N. Hu H.Y. ChenS.Y. Yu L.J. ChenJ.L. Chen G.H. Wu 《Journal of magnetism and magnetic materials》2006
A series of CoxPd1−x (x=0.37–0.85) nanowire arrays have been successfully deposited in a single Co2+/ Pd2+=20:1 solution by applying the various depositing potentials. We found that the nanowires are the composites of CoPd alloy with some Co and Pd clusters, but the overall structure of the composite wires followed the binary phase relation of Pd–Co. The existence of Pd content makes the nanowires structured in FCC phase, except for Co0.85Pd0.15 sample in which some HCP Co phase coexists with the dominating FCC phase. Between Co-rich and Pd-rich nanowires, we found that the optimized composition for CoxPd1−x nanowire is around Co0.73Pd0.27 in which the coercivity (Hc) and squareness (Mr/Ms) have their maximum values consistently. 相似文献
12.
Cobalt-substituted ferrite nanoparticles were synthesized with a narrow size distribution using reverse micelles formed in the system water/AOT/isooctane. Fe:Co ratios of 3:1, 4:1, and 5:1 were used in the synthesis, obtaining cobalt-substituted ferrites (CoxFe3−xO4) and some indication of γ-Fe3O4 when 4:1 and 5:1 Fe:Co ratios were used. Inductively coupled plasma mass spectroscopy (ICP-MS) verified the presence of cobalt in all samples. Fourier transform infrared (FTIR) showed bands at ∼560 and ∼400 cm−1, characteristic of the metal–oxygen bond in ferrites. Transmission electron microscopy showed that the number median diameter of the particles was ∼3 nm with a geometric deviation of ∼0.2. X-ray diffraction (XRD) confirmed the inverse spinel structure typical of ferrites with a lattice parameter of a=8.388 Å for Co0.61Fe0.39O4, which is near that of CoFe2O4 (a=8.394 Å). Magnetic properties were determined using a superconducting quantum interference device (SQUID). Coercivities higher than 8 kOe were observed at 5 K, whereas at 300 K the particles showed superparamagnetic behavior. The anisotropy constant was determined based on the Debye model for a magnetic dipole in an oscillating field and an expression relating χ′ and the temperature of the in-phase susceptibility peak. Anisotropy constant values in the order of ∼106 erg/cm3 were determined using the Debye model, whereas anisotropy constants in the order of ∼107 erg/cm3 were calculated assuming Ωτ=1 at the temperature peak of the in-phase component of the susceptibility curve as commonly done in the literature. Our analysis demonstrates that the assumption Ωτ=1 at the temperature peak of χ′ is rigorously incorrect. 相似文献
13.
Polycrystalline perovskite manganites La0.7−xEuxBa0.3MnO3(x=0.05, 0.1 and 0.15) were prepared by sol-gel method. The prepared samples remain single phase with a perovskite structure, revealed by X-ray diffraction. The structure refinement of La0.7−xEuxBa0.3MnO3(x=0.05, 0.1 and 0.15) samples was performed in the hexagonal setting of the R3¯c space group. The dependence of magnetization M on applied magnetic field H and temperature T was measured carefully near the Curie temperature TC for all the samples. With the increasing Eu content, both the unit cell volume and Curie temperature TC of 298 K has been detected with a maximum of magnetic entropy |ΔSMmax| for the La0.7−xEuxBa0.3MnO3 with x=0.15, reaching a value of 2.3 J/kg K when a magnetic field of 10 kOe was applied and the relative cooling power (RCP) is 46 J/kg. These results suggest that the material may be a suitable candidate as working substance in magnetic refrigeration near room temperature. 相似文献
14.
Magnetocaloric effect (MCE) in fine-grained perovskite manganites of the type La0.67Ba0.33Mn1−xSnxO3 (x=0.05, 0.1 and 0.15) were prepared by the solid-state method. The prepared samples remain single phase and exhibit paramagnetic to ferromagnetic phase transition (TC) at 340, 325 and 288 K for x=0.05, 0.1 and 0.15, respectively. From the measured magnetization data of La0.67Ba0.33Mn1−xSnxO3 compounds as a function of field (2 T), the associated magnetic entropy change close to their respective Curie temperatures and the relative cooling power (RCP) have been determined. Large MCE has been obtained in all samples and |ΔSM|max reached the highest value of 2.49 J/kg K at TC (288 K) for the sample x=0.15, with H=2 T. 相似文献
15.
L.M. da Silva M.C. de Melo A.N. Medina F.G. Gandra 《Physica B: Condensed Matter》2009,404(19):3018-3020
We report on results of X-ray powder diffraction, magnetization and specific heat measurements of the pseudo-ternary (Ce1−xLax)PdIn2 system with x=0; 0.2; 0.4 and 0.6. The results show a linear increase of the unit cell volume and a reduction of the ferromagnetic transition as La content increases. The Debye temperature, Sommerfeld coefficient and crystal field parameters were estimated from specific heat data, and are found to be weakly dependent of the Ce concentration. Also, the variation of magnetic entropy at TC is only weakly dependent on x (ΔS≅0.92Rln2) indicating that TK/TC is approximately constant along the series. The TC and TK behaviors are explained by the variation of the exchange parameter due to the volume change when Ce is replaced by La. Our results indicate that the chemical pressure is the dominant effect rather than the chemical disorder for determining the physical proprieties of the (Ce1−xLax)PdIn2 system. 相似文献
16.
The effects of 60Co (γ-ray) irradiation on the electrical and dielectric properties of Al-TiW-Pd2Si/n-Si Schottky diodes (SDs) have been investigated by using capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements at room temperature and 500 KHz. The corrected capacitance and conductance values were obtained by eliminating the effect of series resistance (Rs) on the measured capacitance (Cm) and conductance (Gm) values. The high-low frequency capacitance (CHF-CLF) method given in [12] as Nss = (1/qA) [((1/CLF) − (1/Cox))−1 − ((1/CHF) − (1/Cox))−1] was successfully adapted to the before-after irradiation capacitance given in this report as Nss = (1/qA) [((1/Cbef) − (1/Cox))−1 − ((1/Cafter) − (1/Cox))−1] for the analyzing the density of interface states. The Nss-V plots give a distinct peak corresponding to localized interface states regions at metal and semiconductor interface. The experimental values of the ac electrical conductivity (σac), the real (M′) and imaginary (M″) parts of the electrical modulus were found to be strong functions of radiation and applied bias voltage, especially in the depletion and accumulation regions. The changes in the dielectric properties in the depletion and accumulation regions stem especially from the restructuring and reordering of the charges at interface states and surface polarization whereas those in the accumulation region are caused by series resistance effect. 相似文献
17.
We synthesized the Mn-doped Mg(In2−xMnx)O4 oxides with 0.03?x?0.55 using a solid-state reaction method. The X-ray diffraction patterns of the samples were in a good agreement with that of a distorted orthorhombic spinel phase. Their lattice parameters and unit-cell volumes decrease with x due to the substitution of the smaller Mn3+ ions to the larger In3+ ions. The undoped MgIn2O4 oxide presents diamagnetic signals for 5 K?T?300 K. The M(H) at T=300 K reveals a fairly negative-sloped linear relationship. Neither magnetic hysteresis nor saturation behavior was observed in this parent sample. For the Mn-doped samples, however, positive magnetization were observed between 5 and 300 K even if the x value is as low as 0.03. The mass susceptibility enhances with Mn content and it reaches the highest value of 1.4×10−3 emu/g Oe (at T=300 K) at x=0.45. Furthermore, the Mn-doped oxides with x=0.06 and 0.2, respectively, exhibit nonlinear magnetization curves and small hysteretic loops in low magnetic fields. Susceptibilities of the Mn-doped samples are much higher than those of MnO2, Mn2O3 oxides, and Mn metals. These results show that the oxides have potential to be magnetic semiconductors. 相似文献
18.
Ca1−xBixNb1−xCrxO3 (x=0.01-0.5) ceramic powders were synthesized using the sol-gel process. The single-phase solids can be presented at x=0.01 and 0.03. The coexistence of orthorhombic perovskite and the secondary phase of BiCrO3 was verified, as presented for x=0.05-0.5. Grains with a micro-cube topography were obtained for x=0.3-0.5. The average grain size is about 0.4 and 1.1 μm for x=0.3 and 0.5, respectively. The highest dielectric constant peak was measured at around 55 °C for x=0.5 and at 75 °C for x=0.3. The high dielectric constant was caused by the formation of barrier layers at the interface of the bi-phase mixed ceramics. Space charge polarization contributed to the observed behavior. 相似文献
19.
Zn1−xNixFe2O4 ferrite nanoparticles were prepared by sol–gel auto-combustion and then annealed at 700 °C for 4 h. The results of differential thermal analysis indicate that the thermal decomposition temperature is about 210 °C and Ni–Zn ferrite nanoparticles could be synthesized in the self-propagating combustion process. The microstructure and magnetic properties were investigated by means of X-ray diffraction, scanning electron microscope, and Vibrating sample magnetometer. It is observed that all the spherical nanoparticles with an average grain size of about 35 nm are of pure spinel cubic structure. The crystal lattice constant declines gradually with increasing x from 0.8435 nm (x=0.20) to 0.8352 nm (x=1.00). Different from the composition of Zn0.5Ni0.5Fe2O4 for the bulk, the maximum Ms is found in the composition of Zn0.3Ni0.7Fe2O4 for nanoparticles. The Hc of samples is much larger than the bulk ferrites and increases with the enlarging x. The results of Zn0.3Ni0.7Fe2O4 annealed at different temperatures indicate that the maximum Ms (83.2 emu/g) appears in the sample annealed at 900 °C. The Hc of Zn0.3Ni0.7Fe2O4 firstly increases slightly as the grain size increases, and presents a maximum value of 115 Oe when the grains grow up to about 30 nm, and then declines rapidly with the grains further growing. The critical diameter (under the critical diameter, the grain is of single domain) of Zn0.3Ni0.7Fe2O4 nanoparticles is found to be about 30 nm. 相似文献
20.
S.K. BarikC. Krishnamoorthi R. Mahendiran 《Journal of magnetism and magnetic materials》2011,323(7):1015-1021
We have studied the effect of Fe substitution on magnetic and magnetocaloric properties in La0.7Sr0.3Mn1−xFexO3 (x=0.05, 0.07, 0.10, 0.15, and 0.20) over a wide temperature range (T=10-400 K). It is shown that substitution by Fe gradually decreases the ferromagnetic Curie temperature (TC) and saturation magnetization up to x=0.15 but a dramatic change occurs for x=0.2. The x=0.2 sample can be considered as a phase separated compound in which both short-range ordered ferromagnetic and antiferromagnetic phases coexist. The magnetic entropy change (−ΔSm) was estimated from isothermal magnetization curves and it decreases with increase of Fe content from 4.4 J kg−1 K−1 at 343 K (x=0.05) to 1.3 J kg−1 K−1 at 105 K (x=0.2), under ΔH=5 T. The La0.7Sr0.3Mn0.93Fe0.07O3 sample shows negligible hysteresis loss, operating temperature range over 60 K around room temperature with refrigerant capacity of 225 J kg−1, and magnetic entropy of 4 J kg−1 K−1 which will be an interesting compound for application in room temperature refrigeration. 相似文献