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1.
Magnetization and Mössbauer studies of TiCu xFe yBe 2-x-y ( x = 0, 0.03, 0.4, y = 0, 0.02) show that TiBe 2 is an enhanced paramagnet, 0.02 Fe or 0.03 Cu reduce the susceptibility. On the other hand, TiCu 0.4Be 1.6 is ferromagnetic ( Tc = 20 K) and 0.02 Fe reduces the magnetization and Curie point ( Tc = 16 K). The magnetic properties of all samples are extremely sensitive to sample preparation and heat treatments. The Mössbauer studies show that the itinerant magnetism resides on the Ti site, all Ti sites have the same local spin density irrespective of local environment. 相似文献
2.
The spin echo spectra of 89Y hyperfine fields in Y(Fe 1−xT x) 3 with low concentration x consist of two main lines and of satellite lines caused by the replacement of the Fe atoms by the T atoms. Values of the magnetic moments of the T atoms are estimated by observing the satellite lines. 相似文献
3.
Lattice spacings, as magnetic susceptibilities, ESR, specific heats, and electrical properties have been measured on the cointercalation compounds of 1T-CdI 2 type host TiS 2, Fe xCo
TiS 2 (0 x
) and (Fe yCo 1−y)
TiS 2(0 y 1). While the interlayer spacings are expanded rather smoothly with increasing the cointercalated Fe metals, the magnetic, thermal, and transport properties depend sensitively on a small amount of the added Fe metals, showing the presence of strong magnetic interactions, or guest-guest interactions between the cointercalated Fe and Co 3d metals in these systems. 相似文献
4.
We present the evolution of magnetic and structural properties of Y 1−xPr xBa 2Cu 3O y ( x0.5 and x=1) single crystals and polycrystalline materials when the oxygen concentration y is varied from under- to overdoping. We have found a monotonous evolution of the Pr Néel temperature for x=1 samples and a maximum of the superconducting critical temperature for the x0.5 samples. The structural properties as detected by X-ray diffraction and Raman spectroscopy show no instabilities when crossing the optimal doping region as was found in the x=0 material. 相似文献
5.
Magnetic and structural characteristics of Pr 2Co 17-based ternaries, in which Co is partly replaced by other transition elements, namely Fe, Mn, Cr, Cu and Al, have been investigated. The objective of the work was to explore the possibility of enhancing the anisotropy of Pr 2Co 17 to the point that it would be useful for permanent magnet fabrication. X-ray diffraction indicates that all the systems studied occur in the rhombohedral Th 2Zn 17 structure. The cell constants increase as Fe, Mn, etc., are introduced in the system, which indicates that substitution occurs in the Co sublattice. The Curie temperatures, Tc, decrease monotonically with increasing x in the order Fe < Cu < Mn < Al < Cr. The saturation magnetization, Ms, increases with increasing x for the Fe system with x 8. For x #62; 8 in the Pr 2Co 17-xFe x system and in all other ternary systems st died, Ms decreases with x, the magnitude of the effect being in the order Cr #62; Al #62; Mn #62; Cu. The rate of decrease is larger than that expected as a simple dilution except for the systems containing Cu. Significant modification of the anisotropy characteristics of Pr 2Co 17 is observed upon substitution. The planar anisotropy of Pr 2Co 17 becomes uniaxial with Fe ( x 4) and Mn ( x 2) substitutions. With Cr and Al substitutions, the plane-seeking tendency of Pr 2Co 17 is significantly weakened. 相似文献
6.
Fe/Fe 1−xSi x/Fe ( x=0.4–1.0) wedge-type epitaxial trilayers with improved homogeneity are grown by co-evaporation from two electron-beam sources. The coupling strengths of the bilinear ( J1) and biquadratic ( J2) coupling terms are derived from Brillouin light scattering (BLS) spectra and longitudinal MOKE hysteresis loops. The total coupling strength J= J1+ J2 increases dramatically with increasing x and reaches values in excess of 6 mJ/m 2. 相似文献
7.
The polarized Raman spectra of Nd 1+xBa 2−xCu 3O 7−δ (−0.023≤ x≤0.107) and Pr 1+xBa 2−xCu 3O 7−δ (0.01≤ x≤0.15) single crystals have been investigated. It was found that the Cu(2) Ag mode softens by 6 cm −1 in Nd 1:2:3 and 4 cm −1 in Pr 1:2:3 as x increases. These frequency shifts cannot be explained by the change in the relevant bond lengths due to Nd(Pr)-substitution for Ba. The variations with x of the two low frequency modes may be affected by change of their hybridization and/or change of their force constants. The linewidths of Ba mode in Pr 1:2:3 are broader than those in Y 1:2:3. This result suggests that the Pr substitution on Ba sites occurred even in a very small value of x. In x( yy)
geometry the relative intensity of the Ba and O(4) modes in Nd 1:2:3 is greater than those in Pr 1:2:3. The difference between Nd 1:2:3 and Pr 1:2:3 in the relative intensity of the Ba and O(4) modes may be produced by the chains. 相似文献
8.
The temperature-composition ( T– x) phase diagram and NFL characteristics in the electrical resistivity ρ( T), specific heat C( T), and magnetic susceptibility χ( T) at low temperatures for the systems U 1−xM xPd 2Al 3 (M=Y,Th) are described. The T– x phase diagram, the NFL characteristics, and the underlying mechanism for the NFL behavior are distinctly different for M=Y 3+ and Th 4+, apparently reflecting the difference in valence of the M atom substituents, and suggesting that U is tetravalent in these two systems. 相似文献
9.
A large positive magnetoresistance (MR) has been found in micro-sized Fe x–C 1−x composites. At a magnetic field of 5 T, the Fe 0.2–C 0.8 composite has the largest MR, 53.8% and 190% at room temperature and at 5 K, respectively. The magnetic field dependence of the MR can be described approximately as MR∝ Bn, and the value of exponent n is determined by the Fe weight concentration and temperature, ranging from 1/4 to 6/4. It appears that Fe x–C 1−x has a linear field dependence of the positive MR at different temperatures. The possible mechanism for the positive MR is discussed. 相似文献
10.
Infinite-layer-type superconductors Sr 1−xLn xCuO 2 are synthesized under high pressure of 3 GPa for Ln=Sm, Gd as well as for Ln=La, Nd. Their chemical and superconducting properties are systematically studied as functions of doping concentration and the kind of lanthanide ion. As a result, it is demonstrated that the variation of these properties with doping concentration is similar for all the examined Ln 3+ ions. The solubility limit lies at x ≈ 0.10. CuO 2 sheets are expanded with increasing x, while their spacing decreases. The Tc onset determined by magnetic measurements remains constant for any doping concentration; only the Meissner fraction increases with increasing x. 相似文献
11.
Superconductivity and crystallographic properties of La 2 − xM xCuO 4 − δ (M = Na, K) are studied. In the La 2 − xM xCuO 4 − δ system, superconductivity is detected for x 0.2. Oxygen content analysis shows that the system has more oxygen vacancies than the La 2 − xSr xCuO 4 − δ system. These oxygen vacancies may reduce the hole concentration, and high Na-doping is needed to produce superconductivity. In the La 2 − xK xCuO 4 − δ system, superconductivity is observed for the first time. Resistivity and magnetic susceptibility measurements show that Tc(onset) is 40 K and the Meissner volume fraction is about 4% for x = 0.7. The system changes from orthorhombic to a tetragonal K 2NiF 4 structure at x ≈ 0.3 and only tetragonal samples show superconductivity. 相似文献
12.
A 27Al nuclear magnetic resonance (NMR) investigation at room temperature of the Pb 1 − xAl xF 2 + x (0 ≤ x ≤ 0.12) solid solution and of the ordered Pb 9Al 2F 24 phase is carried out. Two different types of aluminium ions are identified and their ratio is determined as a function of x. A clustering process based on the formation of column clusters, more and more extended when x increases, is proposed on the basis of results issued from the 19F (Part I) and 27Al NMR investigations. 相似文献
13.
采用溶胶凝胶法制备Bi 1-xCa xFeO 3 (x=0, 0.05, 0.1, 0.15, 0.2)陶瓷样品. X衍射图谱表明所有样品的主衍射峰均与纯相BiFeO 3相符合且具有良好的晶体结构. 随着x的增大, Bi 1-xCa xFeO 3样品的主衍射峰由双峰(104)与(110) 逐渐重叠为单峰(110), 当x ≥0.15时, 样品呈现正方晶系结构; 扫描电镜形貌分析可知, 晶粒由原来的0.5 μm逐渐增大到2 μm. Bi 1-xCa xFeO 3样品介电常数和介电损耗随着x 的增加先增大而后减小. 当f=1 kHz, Bi 0.9Ca 0.1FeO 3 的介电常数达到最大值, 是BiFeO 3的7.5倍, 而Bi 0.8Ca 0.2FeO 3的介电常数达到最小值, 仅仅是BiFeO 3的十分之一. Bi 1-xCa xFeO 3样品所呈现的介电特性是由偶极子取向极化和空间电荷限制电流两种极化机理共同作用的结果. 随着Ca 2+ 的引入, BiFeO 3 样品的铁磁性显著提高. X射线光电子能谱图表明Fe 2+和Fe 3+ 共存于Bi 1-xCa xFeO 3 样品中, Fe 2+/Fe 3+比例随着Ca 2+ 掺杂量的增加而增大, 证明Ca 2+掺杂增加了Fe 2+的含量, 增强BiFeO 3的铁磁特性. 从 M-T曲线观察到BiFeO 3样品在878 K附近发生铁磁相变, 示差扫描量热法测试再次证明BiFeO 3 在878 K发生相变. Ca 2+掺杂使BiFeO 3样品的 TN略有变化而 TM基本不变, 其主要原因是Fe-O-Fe反铁磁超交换作用的强弱和磁结构相对稳定. 相似文献
14.
Magnetic characteristics of Ti-, Zr- and Hf-substituted PrCo 5 alloys have been studied over the temperature range from 77 to 300 K and for applied fields up to 20 kOe. It is established that Ti, Zr and Hf substitute for Pr. Single-phase materials are formed for all values of x up to 0.2 in the system Pr 1−xZr xCo 5 but for x only up to 0.1 for Pr 1−xTi x Co 5 and Pr 1−xHf xCo 5 alloys. Larger amounts of Zr can be substituted if the material is made hyperstoichiometric in Co, e.g., Pr 0.7Zr 0.3Co 5.5. All the alloys show a decrease in magnetic moment and an increase in Curie temperature as x increases. Anisotropy fields decrease as x increases at 295 K. Anomalous behavior is observed at 77 K, suggested that these ternary alloys may have a cone structure at this temperature. 相似文献
15.
We have used linearly and circularly polarized X-rays to determine the magnetic properties of several Tb xFe 1−x amorphous films. Absorption measurements on the M 4.5 edges of Tb and the L 2.3 edges of Fe allowed us to obtain information about the size and direction of local magnetic moments. Our results confirm that linear dichorism in rare earth M 4.5 edges can give useful information about both crystal field and magnetic effects. 相似文献
16.
Oxygen tracer diffusion ( D*) and surface exchange rate constant ( k*) have been measured, using isotopic exchange and depth profiling by secondary ion mass spectrometry (SIMS), in La 1−xSr xFe 0.8Cr 0.2O 3−δ ( x=0.2, 0.4 and 0.6). Measurements were made as a function of temperature (700–1000 °C) and oxygen partial pressure (0.21–10 −21 atm) in dry oxygen, water vapour and water vapour/hydrogen/nitrogen mixtures. At high oxygen activity, D* was found to increase with increasing temperature and Sr content. The activation energies for D* in air are 2.13 eV ( x=0.2), 1.53 eV ( x=0.4) and 1.21 eV ( x=0.6). As the oxygen activity decreases, D* increases as expected qualitatively from the increase in oxygen vacancy concentration. Under strongly reducing conditions, the measured values of D* at 1000 °C range from 10 −8 cm 2 s −1 for x=0.2 to 10 −7 cm 2 s −1 for x=0.4 and 0.6. The activation energies determined at constant H 2O/H 2 ratio are 1.21 eV ( x=0.2), 1.59 eV ( x=0.4) and 0.82 eV ( x=0.6). The surface exchange rate constant of oxygen for the H2O molecule is similar in magnitude to that for the O2 molecule and both increase with increasing Sr concentration. 相似文献
17.
The magnetic phase diagram has been investigated in the C14 type (Zr 1−xNb x)Fe 2 with x0.7 from 93Nb NMR and magnetization measurements. In the compound with x = 0.825 a first order-like transition has been found to occur around 25 K from a canted state with the ferromagnetic moment in the basal plane to a ferromagnetic state with decreasing temperature. 相似文献
18.
通过传统固相反应法制备了钙钛矿锰氧化物(La1-xEux)4/3Sr5/3Mn2O7(x=0,0.15)多晶样品,并且对其磁性和电性进行了研究.磁性测量表明:随着温度的降低,样品经历了一个复杂的转变过程,在温度为T*时经历二维短程铁磁有序转变,在温度为TC时进入三维长程铁磁态.随着Eu的掺杂,T*和TC减小,并且样品(La0.85Eu0.15)4/3Sr5/3Mn2O7在低温区表现出自旋玻璃行为.电性质测量表明:在母体La4/3Sr5/3Mn2O7中La位掺杂Eu后电阻率明显变大,金属绝缘转变温度TMI降低,磁电阻峰值增大.这些影响归因于较小的Eu3+离子替代La3+离子导致平均离子半径减小,晶格发生畸变.此外,较小的Eu3+离子优先占据层间岩盐层的R-site,使La3+,Sr3+,Eu3+离子在(La0.85Eu0.15)4/3Sr5/3Mn2O7中的分布更加有序,所以x=0.15的样品的ρ-T曲线只有一个峰. 相似文献
19.
Magnetic transitions in La(Fe 1−xCo x) 11.4Si 1.6 compounds with x=0–0.08, have been studied by DC magnetic measurements and Mössbauer spectroscopy. The temperature dependence of the Landau coefficients has been derived by fitting the magnetization, M(μ 0H), using the Landau expansion of the magnetic free energy. For x0.02 there is a strongly first-order magnetic phase transition between ferromagnetic and paramagnetic (F–P) states in zero external field and a metamagnetic transition from paramagnetic to ferromagnetic (P–F) above Tc. Increasing the cobalt content drives the F–P transition towards second order and eliminates the metamagnetic transition. 相似文献
20.
New Scheelite-related solid solutions of the compositions Na x/2Bi 1−x/2Mo xV 1−xO 4 (0≤ x≤1) and Bi 1−x/3 Mo xV 1−xO 4(0≤ x≤0.2) have been synthesised by the substitution of Na and Mo at the A and B sites respectively of the ABO 4 type ferroelastic BiVO 4. The phases were characterised using chemical analysis, powder X-ray diffraction, scanning electron microscopy, EDAX, and Raman spectroscopy. While almost a continuous solid solution is obtained for the series Na x/2Bi 1−x/2Mo xV 1−xO 4, the absence of Na at the A-site results only in a narrow stability region for the other series, Bi 1−x/3 Mo xV 1−xO 4 where 0≤ x≤0.2. Raman spectra of selected samples at room temperature also suggest that vanadium and molybdenum atoms are disordered at the tetrahedral sites. 相似文献
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