Narrow Results

The orientational anisotropy of the pseudogap closing field H_pg is investigated in magnetic fields up to 60 T applied parallel (||ab) and normal (||c) to CuO₂ planes in Bi₂Sr₂CaCu₂O_8+y. We find that, in contrast to large field anisotropy related to the orbital motion of Cooper pairs below the upper critical field H_c2, the temperature-independent and small anisotropy of H_pg is due to anisotropy of the g-factor: , indicating correlations only in the spin-channel.

By use of the double-time Green's function method in the cubic-lattice S=1/2 anisotropic antiferromagnetic two-sublattice Heisenberg model, in the Tyablikov approximation, the staggered magnetization m, the correlation function and the static susceptibility are investigated. And the effects of spatial anisotropy are explored. The magnetic properties of this model are found to be dependent of anisotropy.

Anisotropic superconducting properties of new layered intermetallic compounds CaAlSi and CaGaSi with AlB₂ structure are studied. These superconductors show moderate anisotropy with anisotropy parameter determined by both magnetic and transport measurements. Despite the small value of γ, angular dependence of H_c2 in CaAlSi shows cusp-like feature for fields parallel to the superconducting plane, suggesting the presence of two-dimensional superconducting units. By contrast, H_c2(θ) in CaGaSi can be reasonably well explained by the anisotropic GL-model. X-ray diffraction measurements reveal the presence of superstructure along the c-axis in CaAlSi but not in CaGaSi. These findings suggest a close relationship between the anomalous angular dependence of H_c2 and the superstructure. Possible origins of the two-dimensional superconducting units in CaAlSi are discussed.

The magnetic torque of (Cu,C)Ba₂Ca₃Cu₄O_y( (Cu,C)-1234) aligned samples with various carrier concentrations has been measured under a magnetic field of 9 T at 80 K and 90 K. The carrier concentration was determined by Hall effect measurements. From angular dependent torque measurements, the anisotropy ratio γ was estimated using the 3D anisotropic London model. The γvalues decreased from 23 to 10 with an increase in the average Hall number per CuO₂ plane (n_H); however, these samples showed a nearly constant T_c of about 117 K. These results indicate that the anisotropy of (Cu,C)-1234 strongly reflects the doping levels of the outer planes.

We present a full constitutive relation of silicon steel which can describe the anisotropy effect as well. Using a pilot rolling machine, initial silicon strip with thickness of 2.5mm is rolled into sheet with several thicknesses as reduction ratio increases from 10% to 90%. To examine the effect of anisotropy on the stress-strain behavior, the specimen was cut out from the sheet so that the direction of specimen and sheet is 0°, 30°, 45°, 60° and 90°, respectively. A series of tensile test are then performed with the specimens. The stress-strain curves computed from the proposed constitutive relation are compared with the experimental data. Results show that the predicted curves are in overall in a good agreement with measured ones. The work hardening and unstable softening behaviors of silicon steel during rolling are predicted by the proposed full constitutive relation.

In this study, the FEM material model based on the crystal plasticity is introduced for the numerical simulation of deep drawing process of A5052 aluminum alloy sheet. For calculating the deformation and stress in a crystal of aluminum alloy sheet, Taylor's model is employed. To find the texture evolution, the crystallographic orientation is updated by computing the crystal lattice rotation. In order to verify the crystal plasticity-based FEM material model, the strain distribution and the draw-in amount are compared with experimental measurements. The crystal FEM strains agree well with measured strains. The comparison of draw-in amount shows less 1.96% discrepancy. Texture evolution depends on the initial texture.

The exchange–coupling interaction between soft and hard phase layers and the effective anisotropy K_eff have been investigated by putting forward an expression of anisotropy at grain interface, , which is suitable for different coupling conditions in multilayered thin film. The results showed when the dimensions of soft and hard phases are the same (described by b), K_eff increases first, then decreases, and reaches a maximum at a certain value of b with increasing b. For the given hard phase dimension b_h, K_eff decreases monotonously with increasing soft phase dimension b_s. However, for the given b_s, K_eff increases monotonously with the increase of b_h. When the dimensions of soft and hard phases are the same, the variation of K_eff in multilayered thin film is very similar to that of coercivity given by Yang et al. Our results explained the experimental phenomenon better.

The resistivities along c-axis ρ_c(H, T) of ErNi₂ B₂C have been measured with H_⊥ and H_‖c-axis for 2 < T < 300 K and the superconducting upper critical field H_c2(T) curves of ErNi₂B₂C were constructed for each magnetic fields. Our H_c2(T) curves have been compared and discussed with those from ρ_ab(H, T) measurements which explain the anisotropy and its temperature dependence of H_c2(T) are thought to arise from magnetic pair breaking and the anisotropic field dependence of Néel temperature T_N originated from Er⁺³ sublattice.

The polycrystalline La_0.1Lu_xBi_0.9-xFeO₃(x = 0, 0.01, 0.03, 0.05, 0.1 and 0.2) compounds were synthesized by a conventional solid-state reaction method. An unusual exchange bias-like (EB-like) phenomenon was found in this system. Both horizontal shift (H_s) and vertical shift (M_s) are observed simultaneously. Moreover, the horizontal shift displays a similar trend to the vertical shift with the variation of Lu content and the variation of maximum applied magnetic field, revealing that the horizontal shift and the vertical shift are closely correlated. We propose that the horizontal shift may be related to the exchange interaction between two different canted-AFM phases and the vertical shift is related to the large anisotropy of LuFeO₃.

The structural, elastic, chemical bonding, electronic and optical properties of the cubic perovskites RbCaX₃ (X = F, Cl) compounds are obtained by the full-potential linear augmented plane wave (FP-LAPW) method based on the density functional theory. The calculated lattice constants and bulk moduli within GGA agree with previous calculations. It is found that the bulk modulus decreases as the lattice constant increases when traversing from F to Cl in RbCaX₃. Both compounds are found to be elastically stable and anisotropy from the analysis of elastic constants. The analysis of Poisson's ratio, Cauchy pressure and Pugh's index ratio indicate that the RbCaF₃ is brittle compound while the RbCaCl₃ is ductile compound. The Debye temperature for the RbCaX₃ compound evaluates from the average sound velocity. Both compounds are found to have the indirect band-gap (M-Γ) from calculating the band structure. The bonding nature of RbCaX₃ compounds is ionic with a minute covalent bonding. The optical properties are calculated for radiation up to 30 eV. The main peaks of the optical spectra are discussed in terms of the calculated electronic structure. A beneficial optoelectronic and optics technology is predicted from optical spectra.

We study the thermal transport through a quantum spin-$\frac{1}{2}$ heterojunction, which consists of a finite-size chain with two-site anisotropic XY interaction and three-site XZX+YZY interaction coupled at its ends to two semi-infinite isotropic XY chains. By performing the Jordan–Wigner transformation, the original spin Hamiltonian is mapped onto a fermionic Hamiltonian. Then, the fermionic structure is discussed, and the heat current as a function of structural parameters is evaluated. It is found that the magnetic fields applied at respective chains play different roles in adjusting the heat current in this heterojunction. Moreover, the interplay between the anisotropy of the XY interaction and the three-site spin interaction assists to further control the thermal transport. In view of the numerical results, we propose this heterojunction to be an alternate candidate for manipulating the heat current in one-dimensional (1D) systems.

We have performed ab initio investigation of some physical properties of the perovskite TlMnX₃ (X = F, Cl) compounds using the full-potential linearized augmented plane wave (FP-LAPW) method. The generalized gradient approximation (GGA) is employed as exchange-correlation potential. The calculated lattice constant and bulk modulus agree with previous studies. Both compounds are found to be elastically stable. TlMnF₃ and TlMnCl₃ are classified as anisotropic and ductile compounds. The calculations of the band structure of the studied compounds showed the semiconductor behavior with the indirect (M–X) energy gap. Both compounds are classified as a ferromagnetic due to the integer value of the total magnetic moment of the compounds. The different optical spectra are calculated from the real and the imaginary parts of the dielectric function and connected to the electronic structure of the compounds. The static refractive index $n(0)$ is inversely proportional to the energy bandgap of the two compounds. Beneficial optics technology applications are predicted based on the optical spectra.

The structural stability, mechanical properties and Debye temperatures of La-rich La–Ni (LaNi, La₂Ni₃ and LaNi₂) phases were studied by a first-principles method. The formation enthalpy indicates that the La-rich phase is stable. As the La content increases, the enthalpy of formation decreases. The bonding of La–Ni is covalent and metallic. The La-d and Ni-d orbitals contribute mainly at the Fermi level. The mechanical properties indicate that the La-rich La–Ni phases are brittle. La₂Ni₃ has the most prominent anisotropy. The hardness of LaNi, La₂Ni₃ and LaNi₂ are 37.62 GPa, 41.61 GPa and 65.06 GPa, respectively. Those phases have the potential to form a superhard material. LaNi₂ has the highest Debye temperature (232.88 K). LaNi₂ is the most stable among these phases.

${\mathrm{\text{GeSe}}}_2$, a semiconductor with wide bandgap, has attracted wide attention due to its excellent workability in the short-wave region. Here, we reported the mechanical, electronic and optical properties of bulk and monolayer ${\mathrm{\text{GeSe}}}_2$ by using first-principles calculations. Our results show that both Young’s modulus and Poisson’s ratio of the monolayer ${\mathrm{\text{GeSe}}}_2$ exhibit anisotropic behaviors. From the bulk to the monolayer structure, the direct bandgap increases from 2.496 eV to 3.030 eV. Compared to the bulk structure, the monolayer ${\mathrm{\text{GeSe}}}_2$ exhibits the small average effective mass and significant anisotropy in optical absorption, indicating potential optoelectronic applications.

The laser damage resistance of fused silica optics depends significantly on the surface quality. In this work, anisotropic etching with inert ion beams at various ion incident angles was performed to investigate the evolution of the fused silica surface. The results show that the surface is smoothed when the incident angle is below $30^{\circ }$. However, the fused silica surface starts to become coarse owing to the formation of nanostructures on the surface when the incident angle exceeds $30^{\circ }$. Further, ion beam etching at a large incident angle of $70^{\circ }$ removes subsurface defects and less induces nanostructures, resulting in reduction of the surface roughness. The concentrations of impurities and defects are both significantly reduced after ion beam etching. The surface quality, subsurface and surface defects, and surface impurities determine the variation in the laser damage threshold of fused silica with the ion incident angle. The results demonstrate successful application of ion beam etching to improve the laser damage resistant characteristics of fused silica optics. Ion beam etching is a very versatile tool that provides physical erosion to anisotropically mitigate surface damage of fused silica.

The magnetic properties and magnetic anisotropy of epitaxial ultrathin Fe films (4.1–12.7 ML) grown on GaAs (100) are studied using ex situ magnetooptical Kerr (MOKE) loop measurement and Ferromagnetic Resonance (FMR). They give consistent results. The behavior of out-of-plane and in-plane magnetic anisotropy is evaluated from the FMR data. A strong second order out-of-plane anisotropy and an in-plane uniaxial anisotropy are observed to decrease with thickness. A moderate fourth order out-of-plane anisotropy and a four-fold in-plane anisotropy appear for thicker films and increase with thickness. Their origins are discussed.

Fe_xPt_1-x nanoparticles prepared by organometallic synthesis and gas-phase condensation were structurally and magnetically characterised. The effective spin magnetic moments at both the Fe and Pt sites are reduced with respect to the moments in the corresponding bulk material by up to 20% and further decrease with decreasing particle size at the Fe sites. The ratio of orbital-to-effective-spin magnetic moment at the Fe sites increases from 2.1% for 6 nm particles to 3.4% for 3.4 nm particles due to the break of symmetry at the surface. A lowering of the crystal symmetry after the transformation to the chemically ordered L1₀ state yields a ≈ 9% and is accompanied by an enhancement of the coercive field at 15 K from (36±5) mT to (292±8) mT indicating an increase of the anisotropy.

Cobalt thin films deposited by radio frequency sputtering were investigated. Microstructures of the Co films were analyzed by XRD and TEM. The results show that films microstructure varies with the variation of the sputter gas pressure P_Ar. Magnetic properties measured by VSM show that all the films possess relatively high saturation magnetization 4πM_s, and strong in-plane uniaxial magnetic anisotropy field H_k. Co films deposited below 0.3 Pa show soft magnetic properties and its microwave permeability was measured by vector network analyzer in the 0.1–5 GHz range.

In confined space, the thermodynamic potential is shape-dependent. Therefore, the pressure of ideal gases in confined space is anisotropic. We study this anisotropy in a thermodynamic manner and find that the thermodynamic pressures usually depend on the form of deformations, and hence are not equal to each other which is a natural representation of the anisotropic mechanical properties of a confined ideal gas. We also find that the boundary effects are much more significant than the statistical fluctuations under low-temperature and high-density conditions. Finally, we show that there is little difference between the boundary effects in 2D space and those in 3D space.

Following the success of the original BCS theory as applied to superconductivity in metals, it was suggested that the phenomenon of Cooper pairing might also occur in liquid 3-He, though unlike the metallic case the pairs would most likely form in an anisotropic state, and would then lead in this neutral system to superfluidity. However, what had not been anticipated was the richness of the phenomena which would be revealed by the experiments of 1972. In the first place, even in a zero magnetic field there is not one but two superfluid phases, and the explanation of this involves ideas concerning "spin fluctuation feedback" which have no obvious analog in metals. Secondly, the anisotropic nature of the pair wave function, which in the case of the B phase is quite subtle, and the fact that the orientation must be the same for all the pairs, leads to a number of qualitatively new effects, in particular to a spectacular amplification of ultra-weak interactions seen most dramatically in the NMR behavior. In this chapter I review the application of BCS theory to superfluid 3-He with emphasis on these novel features.