共查询到20条相似文献,搜索用时 31 毫秒
1.
G. Litsardakis I. Manolakis C. Serletis K.G. Efthimiadis 《Journal of magnetism and magnetic materials》2007
The effect of Gd substitution in M-type strontium hexaferrites has been examined in two series of samples, (Sr1-xGdx)O·5.25Fe2O3 and Sr1-xGdxFe12-xCoxO19, both prepared by the ceramic method, where x=0–0.40. The samples have been characterized by XRD, VSM and SEM-EDAX techniques. All substituted samples present primarily the hexaferrite structure. Sample (Sr0.95Gdx0.05)O·5.25Fe2O3 is single phase. Formation of impurity phases is affected by stoichiometry and presence of Co. In Sr–Gd samples, coercivity showed a maximum value of 305 kA/m (3.8 kOe) for x=0.20, while remanence and saturation magnetization did not decrease. Coercivity and magnetization in the Sr–Gd–Co series decreased steadily with substitution degree. 相似文献
2.
Perpendicular susceptibility of completely shielded elliptical and rectangular superconducting films
D.-X. Chen C. Navau N. Del-Valle A. Sanchez 《Physica C: Superconductivity and its Applications》2009,469(13):732-735
The perpendicular susceptibility -χ0 of completely shielded elliptical and rectangular superconducting films with different aspect ratios has been calculated accurately. The obtained χ0 may be compared with the measured low-field limit of ac susceptibility to check the quality of superconducting films, and used as a scaling parameter to obtain field amplitude dependent complex critical-state ac susceptibility. 相似文献
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P. Paturi K. Schlesier H. Huhtinen 《Physica C: Superconductivity and its Applications》2009,469(14):839-842
Nanograined YBa2Cu3O6+x (YBCO) targets with grain sizes of 25–45 nm and different densities were prepared with sol–gel method. The properties of the thin films laser deposited from these targets were systematically studied. It was found that most parameters are not clearly affected by the target density, although the surface roughness decreased with target density. A small effect of decreasing Jc with increasing target density was observed, but this can be interpreted as film to film variation. On the other hand, a negative correlation between the accommodation field, B∗, and zero field Jc was observed and B∗ was found to increase with increasing number of lattice defects. Thus target density is found not to have a large effects on the superconducting or structural properties of YBCO thin films. 相似文献
4.
T. Vuletić B. Korin-Hamzić T. Ivek S. Tomić B. Gorshunov M. Dressel J. Akimitsu 《Physics Reports》2006
The quasi-one-dimensional cuprates (La,Y,Sr,Ca)14Cu24O41, consisting of spin-chains and spin-ladders, have attracted much attention, mainly because they represent the first superconducting copper oxide with a non-square lattice. Theoretically, in isolated hole-doped two-leg ladders, superconductivity is tightly associated with the spin gap, although in competition with a charge-density wave (CDW). Indeed, both the gapped spin-liquid and CDW states have been established in the doped spin-ladders of Sr14-xCaxCu24O41, however the relevance of these objects to electronic properties and superconductivity is still subject of intensive discussion. In this treatise, an appreciable set of experimental data is reviewed, which has been acquired in recent years, indicating a variety of magnetic and charge arrangements found in the chains and ladders of underdoped (La,Y)y(S,Ca)14−yCu24O41 and fully doped Sr14-xCaxCu24O41. Based on these data, phase diagrams are constructed for the chains of underdoped systems (as a function of La, Y-substitution), as well as for the chains and ladders of the fully doped ones (as a function of Ca-substitution). We try to reconcile contradictory results concerning the charge dynamics in the ladders, like the hole redistribution between ladders and chains, collective modes and pseudogap, field-dependent transport and the temperature scales and doping levels at which the two-dimensional CDW develops in the ladder planes. The remaining open issues are clearly extracted. In the discussion the experimental results are contrasted with theoretical predictions, which allows us to conclude with two important remarks concerning the nature of the competing CDW and superconducting ground states. A density wave in ladders, characterized by a sinusoidal charge modulation, belongs to the class of broken symmetry patterns, which is theoretically predicted for strongly correlated low-dimensional electron systems; however its precise texture and nature is still an open issue. As for superconductivity, the presence of the spin gap in the normal state points towards d -wave symmetry and magnetic origin of the attractive interaction. However, there is a finite density of mobile quasi-particles that appears for high Ca contents and increases with pressure, concomitantly with increased two-dimensionality and metallicity. For this reason the superconductivity in the doped ladders of Sr14-xCaxCu24O41 which occurs under high pressure cannot simply be a stabilization of the d-wave superconductivity expected for a pure single ladder system. 相似文献
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We have measured the electrical resistance of micrometric to nanometric powders of the La5/8−yPryCa3/8MnO3 (LPCMO with y=0.3) manganite for hydrostatic pressures up to 4 kbar. By applying different final thermal treatments to samples synthesized by a microwave assisted denitration process, we obtained two particular grain characteristic dimensions (40 nm and 1000 nm) which allowed us to analyze the grain size sensitivity of the electrical conduction properties of both the metal electrode interface with manganite (Pt/LPCMO) and the intrinsic intergranular interfaces formed by the LPCMO powder, conglomerate under the only effect of external pressure. We also analyzed the effects of pressure on the phase diagram of these powders. Our results indicate that different magnetic phases coexist at low temperatures and that the electrical transport properties are related to the intrinsic interfaces, as we observe evidences of a granular behavior and an electronic transport dominated by the Space Charge limited Current mechanism. 相似文献
7.
The effects of disorder and incipient magnetism in MgC(Ni1-xTx)3 (T≡Fe, Co or Cu) alloys are studied using coherent-potential approximation and Ginzburg–Landau coefficients. The first-principles, local-density-functional-based calculations for substitutionally disordered Fe and Co impurities in the Ni sub-lattice of MgCNi3, in low concentrations, show that incipient magnetism resides in these materials. The overestimation of the calculated magnetic properties points to the limitations of the local-density approximation. However, using a phenomenological approach based on Ginzburg–Landau coefficients and the fixed-spin moment method, we show that MgC(Ni1-xTx)3 alloys remain paramagnetic. At expanded volumes, we also find the possibility of a ferromagnetic state for MgC(Ni0.95Fe0.05)3 and MgC(Ni0.90Co0.10)3 alloys. 相似文献
8.
Inverted hysteresis loops (IHL) of negative net area have been measured for some films using vibrating sample magnetometer (VSM), SQUID magnetometer or magneto-optic Kerr effect magnetometer. All of the IHL were observed in the field direction along the hard axis. An IHL violates the thermo-mechanical second law. This work points out that an IHL arises when |Mx|?|Mz| (Mx and Mz: the parallel and normal to the field direction components of magnetization vector) if the sample is set at certain inappropriate positions in VSM and SQUID magnetometer experiments, and the sense voltage is solely attributed to Mx while it also relates to Mz. 相似文献
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G. Narsinga Rao Saibal Roy Chung-Yuan Mou J.W. Chen 《Journal of magnetism and magnetic materials》2006
We have investigated the magnetotransport and magnetic properties on polycrystalline samples of Sr2−xLaxFeMoO6 (x=0, 0.2, 0.4, 0.6, 0.8 and 1.0). The magnitude of intergrain tunneling magnetoresistance with low magnetic field of 0.88 T for x=0.2 and 0.4 samples are as large as 5% and 7% at room temperature and 13% and 10% at 10 K, respectively. The increase of coercivity (Hc), ratio of remanent magnetization with respect to saturation magnetization (Mr/Ms), high saturation fields, and reduction of the saturation magnetization indicate that random disorder of spin orientation is mainly responsible for enhancement of the low-field magnetoresistance for samples with x?0.4. Whereas rapid drop of Hc, Mr/Ms, Mr, and saturation fields for samples with x>0.4 signifies the growth of antiphase boundary, which gives rise to lower values of low-field MR. 相似文献
11.
Temperature dependencies of magnetic susceptibility and electric resistivity of Co-based metallic glasses (MGs) of the general composition Co(72-x)Mex(Si,B)28(Me=Fe,Cr,Si:B=18:10) have been studied up to 950 K. The studied MGs were found to be ferromagnets at the room temperature and their Curie point TC ranges within 260–560 K depending on the dopant contents. At the temperatures higher than TC, a wide paramagnetic region exists. The regularities of magnetic moment variation upon Cr doping evidence a formation of antiferromagnetic clusters, which determine the anomalous behavior of resistivity. 相似文献
12.
This study employs the self-consistent Green's function method to study the magnetic properties of diluted CoxCu1-x alloys from a consideration of their spin dynamics characteristics. The numerical results show that in dilute cobalt concentrations (i.e. x?0.4), the critical temperatures vary linearly with x for different itinerant carrier concentration conditions. Interestingly, the carrier concentration does not affect the degree of dependency of the temperature on the cobalt concentration when the carrier concentration is less than the atomic number concentration of the alloy. 相似文献
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K. Kamishima C. Ito K. Kakizaki N. Hiratsuka T. Shirahata T. Imakubo 《Journal of magnetism and magnetic materials》2007
We have found that the initial permeability μ′ of Co2Z ferrite is improved by the substitution of Ti4+ and Zn2+ ions for Fe3+ ions. The substituted sample of Ba3Co2TixZnxFe24-2xO41 with x=0.85 has a maximum μ′ of 24, which is twice as large as that of the non-substituted sample with x=0. The particle size and shape are changed by the substitution. This is influential in the densification and the preferential orientation of a toroidal-shape sample, which results in the improvement of μ′. 相似文献
15.
V.Yu. Ivanov A.A. Mukhin V.D. Travkin A.S. Prokhorov A.M. Kadomtseva Yu.F. Popov G.P. Vorob’ev K.I. Kamilov A.M. Balbashov 《Journal of magnetism and magnetic materials》2006
Multiferroic ground states with a spatially modulated antiferromagnetic structure and electric polarization have been revealed in Eu1−xYxMnO3 (0.2?x?0.5) single crystals. While the slightly substituted (x?0.1) compounds exhibited a transition from the incommensurate (IC) to the canted antiferromagnetic (CAF) state at TCA<TN, the transitions from IC to commensurate ferroelectric (C/FE) phase were observed at Tlock<TN for x>0.2. Various phase transitions were observed in the magnetic fields up to 250 kOe along a, b, c axes by magnetization, magnetostriction and electric polarization measurements which show an existence of a spontaneous electric polarization below Tlock. 相似文献
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Bi doped lanthanum manganites with the chemical composition of La0.67−xBixCa0.33MnO3 (x=0, 0.05, 0.1, 0.2) were prepared by the standard solid-state process. The Curie temperatures were measured to be 267 K for x=0, 248 K for x=0.05, 244 K for x=0.1 and 229 K for x=0.2 samples. It was found that the maximum value of the magnetic entropy change ∣ΔSm∣ has reached the highest value of 6.08 J/kg K at 3 T for the composition with x=0.05. Nearly the same maximum entropy change was observed for the x=0 sample. A large decrease in the magnitude of the entropy change was observed for the x=0.2 sample. 相似文献
18.
W.J. Li B.C. ZhaoR. Ang W.H. SongY.P. Sun Yuheng Zhang 《Journal of magnetism and magnetic materials》2006
A series of the double-doping samples La(2+4x)/3Sr(1−4x)/3Mn1−xCuxO3(0?x?0.2) with the Mn3+/Mn4+ ratio fixed at 2:1 have been prepared. The structural, magnetic, transport properties and magnetoresistance of the series samples have been investigated. It is found that no apparent crystal structure change is introduced by Cu doping up to x=0.20. But the Curie temperature TC and magnetization M are strongly affected by Cu substitution. A remarkable magnetotransport behavior, characterized by double bumps, is observed, and an obvious low-temperature upturn is found in the range of 0.07?x?0.12. As a result, the temperature range of colossal magnetoresistance (CMR) is greatly broadened. Moreover, it is found that the room temperature magnetoresistance (MR) of double-doping samples is obviously larger that the undoped La2/3Sr1/3Mn1−xCuxO3 at 300 K, which can give a guide for the adequate selection of the room temperature CMR materials. 相似文献
19.
The three-dimensional spin-1 Ising superlattice consisting of two different ferromagnetic materials with two different crystal fields Δ1 and Δ2 is considered in the mean field approximation. The phase diagrams are considered in the (t,d2) plane for different ranges of variation of d1(t=T/J,d1=Δ1/J, d2=Δ2/J are the reduced temperature and crystal fields respectively). The phase diagrams exhibit a variety of multicritical points and reentrant and double reentrant behaviours. They are found to depend qualitatively and/or quantitatively on the thicknesses of the materials in a supercell. This has direct consequences on the nature of the magnetic states of superlattices with different thicknesses. 相似文献