共查询到20条相似文献,搜索用时 15 毫秒
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Pradeep Kumar 《Journal of Low Temperature Physics》1980,38(5-6):655-666
A phenomenological formulation of the enhancement of the susceptibility of liquid 3He in contact with a dielectric surface is presented. The effective Hamiltonian includes a surface term consisting of both the quadratic and the quartic dependence on the surface order parameter. The partition function for this system is calculated using a novel application of the transfer matrix methods. We find a susceptibility that contains the Curie-Weiss-like surface contribution as well as the appropriate field dependence in agreement with experiments. In addition, we find a weak temperature-dependent anomaly in specific heat as well.Nordita Visiting Professor. 相似文献
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B. G. Tagiev O. B. Tagiev R. B. Dzhabbarov N. N. Musaeva U. F. Kasumov 《Inorganic Materials》2000,36(1):3-5
The photoluminescence of Ca4Ga2S7:Ce3+ and Ca4Ga2S7:Pr3+ was studied. Ca4Ga2S7 was found to have an fcc structure witha = 5.67 Å. The photoluminescence of the rare-earth-doped materials is due to Ce3+ and Pr3+ intracenter transitions. The lifetimes of Ce3+ and Pr3+ excited states fall in the range 10-5 to 10-7 s, and the frequency factor is 1011-10-12 s-1 相似文献
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Patrice Fivat Jean-Marc Triscone Øystein Fischer 《Journal of Superconductivity and Novel Magnetism》1994,7(1):181-185
Multilayer structures containing 24 Å thick DyBa2Cu3O7 layers, separated by 96 Å of an (Y0.6Pr0.4)Ba2Cu3O7 alloy, are studied to investigate the effect of coupling on vortex dynamics. With the magnetic field perpendicular to theab plane, and as a function of the number of superconducting layers in the structure, we find that the activation energy for flux motion increases, first linearly, and then saturates. This linear increase is taken as evidence that pancake vortices belonging to different DyBa2Cu3O7 layers are stacked and have a coupled motion. Above a characteristic number of superconducting layers,N c , shear of the vortex structures becomes important and the thermally activated process only displaces a stack ofN c pancake vortices, meaning that the vortex lattice is turning three dimensional. In these structures we findN c to be 2 to 3. 相似文献
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J. H. Hetherington 《Journal of Low Temperature Physics》1987,66(3-4):145-154
The classical analog of the Hamiltonian proposed for3He spins by Stipdonk and Hetherington is studied. First- and second-order phase transitions similar to those found experimentally are obtained. This paper introduces the use of a Gaussian ensemble rather than a canonical ensemble in the Monte Carlo method. This ensemble is equivalent to the canonical ensemble in the limit of large systems except in the energy range inside of a first-order transition. This new method has general applicability, but is especially useful for studying first-order transitions, since it can eliminate the problem of hysteresis associated with them. 相似文献
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E. Sherman R. Li R. Feile H. Adrian G. Jakob 《Journal of Low Temperature Physics》1995,99(3-4):263-265
An extra peak was observed in the region of 290–320 cm–1 of Raman spectra of a high quality (001) (Y2Pr1)(Ba2Cu3O7) superlattice in Z(X,Y)Z geometryat low temperature. It was identified as an even combination of B1u vibrations in Y-subcells. We propose an asymmetric field mechanism for the Raman intensity of this extra phonon.This work is supported by Deutsche Forschungsgemeinschaft (SFB 252). E.S gratefully acknowledges the support by Alexander von Humboldt Foundation. 相似文献
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Two representative superconductors, UPt3 and Sr2RuO4, are comparatively studied on the basis of a general symmetry argument. The existing experimental data set for both systems strongly and commonly points to a triplet pairing. For the former, heavy fermion material, UPt3, a non-unitary bipolar state is the most possible candidate, whereas for the latter system, Sr2RuO4, determination of a precise pairing symmetry class, either unitary or non-unitary, is debated. 相似文献
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The suppression of the superconductivity by praseodymium in La1−x
Pr
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CaBaCu3O7 may be explained in terms of the difference in the electronic or crystal structure between these compounds. Three compositions
with x=0.0, 0.5, 1.0 were, therefore, investigated by X-ray diffraction in order to determine the unit-cell dimensions at room temperature
as well as at lower temperatures down to 5 K. The results showed no considerable changes in the orthorhombic unit-cell dimensions
on decreasing the temperature to 5 K. Unit-cell volumes at low temperatures were 0.99 of the room temperature values. The
intensity sequence of reflections in the diffraction pattern was the same for all samples throughout the range of temperature
studied. 相似文献
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Pr3+摩尔浓度对CaTiO3:Pr3+红色长余辉材料的影响 总被引:7,自引:0,他引:7
制备了不同Pr^3 摩尔浓度下的CaTiOs:Pr^3 红色长余辉材料,测量了磷光体的的初始亮度、余辉曲线、激发光谱和发射光谱、热释光曲线。研究发现CaTiO3:Pr^3 合适的Pr^3 摩尔浓度为0.1%—0.2%,在该摩尔浓度下,材料具有较好初始亮度和余辉时间。 相似文献
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最近发现的层状铁磁材料吸引了研究者的广泛兴趣,但是其有限的数量严重阻碍了进一步的发展.作为一个更大的家族,层状反铁磁材料为加深对基本磁性物理的理解和推动高性能自旋电子学的应用提供了一个出色的平台.本文中,我们选取了过渡金属磷三硫族化合物中代表性的反铁磁CoPS3材料,并通过系统的第一性原理计算证实压力或载流子掺杂可有效... 相似文献
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M. Malinowski I. Pracka B. Surma T. ?ukasiewicz W. Woliński R. Wolski 《Optical Materials》1996,6(4):305-312
The spectroscopic properties of trivalent praseodymium (Pr3+) doped SrLaGa3O7 (SLG) crystals have been investigated at various temperatures. Absorption, emission, excitation and lifetime measurements have been performed and discussed in the framework of the Judd-Ofelt approach. Stimulated emission cross sections for the strongest transitions of Pr3+ ion have been calculated. Stimulated emission has been observed for the first time in Pr3+ doped SLG crystal, we have obtained laser operation at 488 n, at cryogenic temperatures and at 645 nm at room temperature. 相似文献
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溶胶-凝胶法制备Fe掺杂ZnO基稀磁半导体的结构与磁性 总被引:1,自引:0,他引:1
采用了添加抗坏血酸作为还原剂的改良溶胶-凝胶法制备了单相的稀磁半导体Zn1-xFexO(x=0.01、0.05、0.07、0.10) 粉末.X射线衍射谱(XRD)显示所有Zn1-xFexO样品在室温下都呈现出P63mc的六角晶格结构,同时单位晶胞体积呈现出随着Fe离子掺杂量的提高而增大的趋势.X射线光电子能谱(XPS)证明在Zn1-xFexO晶格中的掺杂元素Fe主要以Fe2 的方式存在.比饱和磁化强度(σs)随Fe掺杂量的增加而提高,并在样品Zn0.90Fe0.10O中获得最大值0.43Am2/kg,定性地解释了铁磁性的来源. 相似文献
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Xianmin Zhang Chunyan Cao Chenghua Zhang Shiyao Xie Guangwen Xu Jiahua Zhang Xiao-jun Wang 《Materials Research Bulletin》2010,45(12):1832-1836
Red-emitting CaTiO3:Pr3+ phosphors are fabricated using a solid state method and structurally characterized by X-ray diffraction and field emission scanning electron microscopy. The optical properties are investigated using photoluminescence emission, excitation, photoluminescence decay curves, diffused reflectance and thermoluminescence spectra, and persistent phosphorescence decay curves. The optimal fabrication temperatures for photoluminescence and persistent phosphorescence are found at 1200–1300 °C for photoluminescence and 1400 °C for persistent phosphorescence. The energy storage traps for persistent phosphorescence in the system are analyzed based on the dependence of photoluminescence and persistent phosphorescence on sintering temperature. The distribution of energy storage traps is further characterized by thermoluminescence spectra and the parameters of the traps are calculated. Oxygen vacancies as the main trapping centers play the key role for persistent phosphorescence in CaTiO3:Pr3+. 相似文献