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1.
A comparison has been made of irreversibility temperature determined by four different methods in few specimens of lead (type-I)
and niobium (type-II). The merger ofM
ZFC(T) andM
FC(T) curves giveT
r(H) values lower than those evident from vanishing the hysteresis in isothermal DC magnetization. The identification of peak
temperature inx″
H
(T) data withT
r(H) is appropriate only if the contribution from changes in the normal state electrodynamics can be isolated and the peak is
narrow. The appearance of differential paramagnetic effect inx′
H
(T) data is adequate to imply reversibility, however, its efficacy to precisely locate irreversibility line remains to be established. 相似文献
2.
Cubic ZnMnO3 powder in the form of well-crystalline nanoflakes have been synthesized at low temperatures from a nitrate precursor. The electrical properties of cubic ZnMnO3 samples have been established by DC resistivity (ρ) and thermo-electric power (Seebeck coefficient) measurements on a pressed pellet. The material exhibits insulator behavior with 0.7 eV acceptor ionization energy in the measured temperature range of 170-300 K. The thermo-electric power indicates a positive sign of the charge carriers. The obtained material exhibits a superparamagnetic signature with a blocking temperature of 9 K and the ZFC-FC splitting temperature of 15 K. 相似文献
3.
B. Aslibeiki 《Current Applied Physics》2014,14(12):1659-1664
Nano-crystalline MnFe2−xAgxO4 (x = 0, 0.1, 0.2, 0.3 and 0.6) samples with average grain size of 4–7 nm were synthesized by a simple method based on decomposition of metal nitrates in presence of citric acid. The samples were characterized by different structural, magnetic and electrical measurements. Rietveld refinement of X-ray diffraction data confirmed cubic spinel structure of the samples. Results show that Ag doping decreases the crystallite size, magnetization and coercivity of nanoparticles. By increasing the Ag content in the samples the saturation magnetization shows interesting temperature dependent behavior. It was realized that magnetization of smaller particles show higher sensitivity to temperature variations than larger particles. DC electrical resistivity measurements in the temperature range of 300–650 K show that the resistivity first increases and then decreases by increasing the Ag content in the samples. Curie temperature (Tc) and polaron activation energy in ferromagnetic and paramagnetic regions were estimated by using resistivity curves. 相似文献
4.
CoTb0.03Fe1.97O4 ferrite and poypyrrole (PPy) polymer nano composites were prepared by mixing the nano crystalline ferrite with poypyrrole (PPy) by following the solid state reaction synthesis route. The XRD patterns of CoTb0.03Fe1.97O4 spinel ferrite powders and polymer (PPy) exhibited single phase spinel structure. The amorphous nature of PPy was evidenced by the broad peaks of XRD patterns. The surface morphology unfolded heterogeneous distribution in composites and ferrite. The grains in ferrite were spherical in shape with clear boundaries. The morphology was appreciably altered by the inclusion of ferrite contents. The higher activation energy and resistivity aroused due to blocking of conduction mechanism owing to nanoparticles embedded in the PPy matrix. A downfall in the dielectric loss of the composites is observed as the frequency of the applied field is increased. The incorporation of ferrite contents optimized the magnetic parameters of the composites. The enhanced coercivity (Hc) of these nanocomposites might be beneficial for memory devices. 相似文献
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6.
Spontaneous magnetization and resistivity jumps in bilayered manganite (La0.8Eu0.2)4/3Sr5/3Mn2O7 single crystals 下载免费PDF全文
Owing to the inhomogeneous state resulting from the doping of a small number of Eu ions into Laa/3Sr5/3Mn2O7, from the resulting single crystal (La0.8Eu0.2)a/3Sr5/3Mn2O7 we have observed the magnetization jump, the resistivity jump, as well as the relaxation phenomena. For (Lao.sEuo.2)a/3Sr5/3Mn2O7, it has a very delicate ground state due to the interplays among spin, charge, orbital, lattice degrees of freedom. Consequently, the magnetization state is sensitive to temperature, magnetic field, as well as time. Meanwhile, the evolution of the magnetization with time shows a spontaneous jump when both the temperature and the magnetic field are constant. Similar step-like behaviours are also observed in resistivity. All these results suggest that Eu doping can greatly modulate the physical properties of Laa/3Sr5/3Mn2O7 and cause such interesting behaviours. 相似文献
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8.
Ho and Ti co-doped BiFeO_3 multiferroic ceramics with enhanced magnetization and ultrahigh electrical resistivity 下载免费PDF全文
Bi0.9Ho0.1Fe0.95O3 and Bi0.9Ho0.1Fe0.9Ti0.05O3 ceramics were prepared and compared to reveal the effects of Ho and Ti codoping in BiFeO3. X-ray diffraction indicated that both ceramics had a high rhombohedral perovskite phase content, and microstructural analyses showed that the grains of the Bi0.9Ho0.1Fe0.9Ti0.05O3 ceramics were much smaller than those of Bi0.9Ho0.1Fe0.95O3. An electrical resistivity of more than 1 × 1014?·cm at room temperature, and a magnetic hysteresis loop with a remnant magnetization 2Mr of ~ 0.485 emu/g were obtained for Bi0.9Ho0.1Fe0.9Ti0.05O3; both were much higher than those of Bi0.9Ho0.1Fe0.95O3. Changes in the defect subsystem of BiFeO3 induced by Fe-deficiency and(Ho,Ti) codoping are proposed as being responsible for the improvement in the properties. 相似文献
9.
Ho and Ti co-doped BiFe03 multiferroic ceramics with enhanced magnetization and ultrahigh electrical resistivity 下载免费PDF全文
Bio.9HOo.lFeo.9503 and Bio.9HOo.lFeo.9Tio.0503 ceramics were prepared and compared to reveal the effects of Ho and Ti codoping in BiFeO3. X-ray diffraction indicated that both ceramics had a high rhombohedral perovskite phase content, and microstructural analyses showed that the grains of the Bio.9HOo.lFeo.9Tio.0503 ceramics were much smaller than those of Bio.9HOo.lFeo.9503. An electrical resistivity of more than 1 × 1014.cm at room temperature, and a magnetic hysteresis loop with a remnant magnetization 2Mr of 0.485 emu/g were obtained for Bi0.9HO0.1Fe0.9Ti0.0503; both were much higher than those of Bio.9Hoo.1Feo.9503. Changes in the defect subsystem of BiFeO3 induced by Fe-deficiency and (Ho,Ti) codoping are proposed as being responsible for the improvement in the properties. 相似文献
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11.
In an exchange-bias system, the barriers with intrinsic potential energy may be asymmetric due to unidirectional anisotropy. Based on the Stoner-Wohlfarth model, we show that the asymmetric barriers may lead to four kinds of dynamical process underlying the hysteresis-loop measurement. These kinds of dynamical processes are different in a topology-like property, which can be controlled by the orientation of the external field. In our study, a new analysis approach has been proposed to reveal the dynamical behaviors of magnetization reversal. With this approach, coercivity, exchange-bias field, and asymmetry of hysteresis loops can be quantitatively obtained. 相似文献
12.
M. Siva Ram PrasadB.B.V.S.V. Prasad B. RajeshK.H. Rao K.V. Ramesh 《Journal of magnetism and magnetic materials》2011,323(16):2115-2121
Polycrystalline Ni0.65−xCdxZn0.35Fe2O4 ferrites with x varying from 0.00 to 0.20 in steps of 0.04 have been prepared by conventional ceramic route. Calcination and sintering of samples were performed at 950 and 1250 °C for 4 and 2 h, respectively. The prepared samples were characterized by powder X-ray diffraction. The observed modifications in structure and increase in lattice constant are attributed to the difference in ionic radius of substituted Cd2+ ion and displaced Ni2+ ion. The room temperature specific saturation magnetization and Curie temperature are observed to decrease continuously with decrease in cadmium content and are attributed to the decline of A-B exchange interaction. The monotonic increase in initial permeability and decrease in magnetic loss are observed with cadmium concentration. An increase in dc electrical resistivity is observed up to x=0.12 of cadmium followed by a continuous decrease. The variation of electrical resistivity with temperature was measured in the temperature range of RT-140 °C and the corresponding activation energies for conduction obtained from the log ρ vs 1/T graphs. 相似文献
13.
We present DC and low frequency AC magnetization measurements on various RBa2Cu3O7 superconductors. We identify features intrinsic to these compounds, and establish the features originating from intergranular
links in sintered pellets. The isothermal magnetization curves, and the temperature dependence of magnetization in field-cooled
and zero field-cooled states are shown to be consistent with the calculations done following a recent extension of Bean’s
model. Low field anomalies predicted within this model are observed, and yieldH
c1 values of a few Oe. These values are shown to be consistent with the temperature variation of magnetization. A comparison
is made with the other existing data and it is demonstrated that earlier quoted values ofH
c1 are gross overestimates. 相似文献
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M. Penchal Reddy W. Madhuri N. Ramamanohar Reddy V.R.K. Murthy R. Ramakrishna Reddy 《Journal of magnetism and magnetic materials》2010,322(19):2819-2823
The low temperature microwave sintered NiCuZn and MgCuZn ferrites with compositions Ni0.35Cu0.05Zn0.60Fe2O4 and Mg0.35Cu0.05Zn0.60Fe2O4 were synthesized by conventional mixed oxide method. NiCuZn and MgCuZn ferrite samples obtained showed better sintered densities at 950 and 900 °C, respectively. The scanning electron micrographs of both the ferrite samples appear to be very much similar. The magnitude of initial permeability of MgCuZn ferrite samples is found to be obviously higher than those of NiCuZn ferrite samples at all sintering temperatures. This is mainly due to the fact that MgCuZn ferrite has smaller magnetocrystalline anisotropy constant and magnetostrictive constant. NiCuZn ferrites have higher saturation magnetization than MgCuZn ferrites, which is due to the higher magnetic moment of NiCuZn ferrites. Our results indicate that the microwave sintering method seems to be a potential technique in the MLCI technology. 相似文献
17.
The polycrystalline samples La0.67Ca0.33Mn(1?x)Fe x O3 (x?=?0.00,?0.01,?0.03, and 0.1) have been grown in single phase by solid state route. The analysis of the reaction has been done by thermogravimetry and differential thermal analysis measurements. DC electrical resistivity measurements have been carried out down to 15?K. The samples with x?=?0.00, 0.01, and 0.03 exhibit metal–insulator (MI) transition at temperatures 221.5?K, 217?K, and 215?K respectively, whereas the sample with x?=?0.1 is insulating in nature for entire temperature range. Interestingly, the electric transport properties of these samples are not consistent with their magnetic phase transitions and the samples show MI transition at a temperature, T MI, which is significantly lower than the paramagnetic to ferromagnetic transition temperature (T c). The resistivity data below T MI has been analyzed using the empirical relation ρ?=?ρ0?+?ρ1 T n and the data above this temperature has been analyzed using two existing models, Mott's variable range hopping model and spin polaronic conduction model. 相似文献
18.
T. S. Orlova A. M. Mavlyutov A. S. Bondarenko I. A. Kasatkin M. Yu. Murashkin R. Z. Valiev 《哲学杂志》2016,96(23):2429-2444
An ultrafine grained (UFG) structure has been obtained in commercial purity Al by high-pressure torsion (HPT). Changes in microhardness and electrical resistivity of the UFG material after annealing at various temperatures within a range of 363–673 K have been investigated in correlation with the microstructure evolution. It has been shown that annealing at 363 K leads to substantial decrease in the electrical resistivity while keeping high microhardness level and approximately the same average grain size. The contributions from the various microstructural units (vacancies, dislocations, grain boundaries (GBs)) to the electrical resistivity were analysed. It was shown for the first time that a non-equilibrium state associated with strain-distorted grain boundary (GB) structure strongly affects electrical resistivity of UFG Al. The resistivity of non-equilibrium GBs in UFG structure formed by HPT was evaluated to be at least 50% higher than the resistivity of the thermally equilibrium GBs in a coarse-grained structure. 相似文献
19.
基于CFETR工程设计,使用TOKSYS建立了CFETR极向场线圈、真空室壁和包层结构的等效二维模型.在三种平衡的等离子体位形下,分析了包层结构整体等效电阻率和极向不同位置的等效电阻率对等离子体垂直位移增长率的影响.结果表明,垂直位移增长率随着包层整体等效电阻率的增加近似线性增大;降低极向±60°附近的等效电阻率,能减... 相似文献
20.
针对电动汽车锂离子电池组在工作过程中出现的能量不一致现象,设计了一种基于反激式直流变换器的主动均衡电路,包括电源转换、信号采集、驱动电路以及均衡器4个模块。研究了均衡系统的拓扑结构和工作原理以及控制策略,阐述了反激式直流变换器与锂离子电池的建模方法,针对电池组8种典型的非均衡工况,进行了混合策略下的5 kHZ高频仿真实验,实验用电池SOC从44.3%到55.7%均有涉及,仿真与实验结果误差均在10%以内,验证了PSIM仿真电路与同轴多绕组变压器与电池建模方法以及混合控制策略的正确性。 相似文献