Narrow Results

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.

We present the scaling law of the pinning force F_P in intermediate and high temperature superconductors, the factors which influence its field and temperature dependence, the limitations imposed by the enlarged anisotropy and high operating temperatures, giant creep included. The theoretical developments which incorporate the new features of these classes of superconductors, most of them based on the Anderson–Kim theory, prove to be a useful source of information relative to the nature of the pinning and the characteristic fields. The use of models based on thermal activation integrates into scaling the tail of pinning force and also substantiates the use of the irreversibility field H_irr as scale field. Finally, the data on scaling law in the two class of superconductors are presented and discussed.

Recent investigations have revealed that the Ruddlesden–Popper series (A_n+1B_nO_3n+1) and the layered perovskite LnBaCo₂O_5+δ (Ln = rare-earth cations) are promising as cathodes for intermediate temperature solid oxide fuel cells. For these to be economical the oxygen diffusion must be maximized. Based on atomistic simulations, we propose strategies for optimizing oxygen diffusion in these materials by modifying the oxygen stoichiometry, the composition and cation disorder. The present investigation is focused on La₂CoO_4+δ and GdBaCo₂O_5+δ and the results are discussed in view of recent experimental and theoretical studies.

CoFeB nanotubes were fabricated by electroless plating in magnetic field using anodized aluminum oxide template, and the structural and magnetic properties of CoFeB nanotubes were investigated. It is found that some nano-scale particles form on the wall of nanotubes. Both coercivity ratio and squareness ratio of out-of-plane to in-plane are significantly changed by the applied magnetic field during electroless plating, which indicates that directional ordering in amorphous CoFeB nanotubes are achieved during electroless plating under magnetic field. The results show that the applied field impacts the magnetic anisotropy of amorphous nanotubes. The anisotropy is stronger with the magnitude of applied field increasing.

Anisotropies of different conductivity mechanisms in Y_1-yPr_yBa₂Cu₃O_7-δ single crystals in a wide range of praseodymium concentrations are reported, assuming a transition from the metallic conductivity to the semiconductor-like regime, in conjunction with the fluctuation conductivity within the 3D Aslamazov–Larkin model. The T_c anisotropy grows with increasing y, with a most drastic rise when approaching the non-superconducting composition. As the praseodymium concentration increases, the ideal resistance anisotropy passes through a maximum at y ≈ 0.19. The temperature dependence of the semiconductor-like resistance anisotropy exhibits a maximum associated with variable-range jumps along the c-axis. The temperature dependence of the fluctuation conductivity anisotropy passes through a maximum due to a significant anisotropy of the coherence length.

Following up published works in which we studied and experimentally verified the assumptions of the theory of "Deformed Space-Time" in relation to piezonuclear emissions, and according to previous experiments of sonication by ultrasounds performed on solid materials with high density, cylindrical bars of AISI 304 steel have been sonicated by ultrasounds of the power of 330 Watts and frequency of 20 KHz. We verified by means of passive detectors CR39 (PADC) pulsed emissions of neutrons. In this work, following a recent proposal, it was decided to perform a stereoscopic measurement of neutron emission. It has been verified that they are characterized by a distribution which is anisotropic and asymmetric in the space. The work shows a wide and accurate description of the experiment and the results of neutron emissions, and we stress that there exist two directions corresponding to maximum emission (maximum dose) and zero emission (null dose).

The transverse electrical resistance of HoBa₂Cu₃O${}_{7-\delta }$ single crystals is investigated in the temperature range $T_c-300\mathrm{\text{K}}$ for optimally-doped $(T_c\approx 91\mathrm{\text{K}})$ and oxygen-poor $(T_c\approx 51\mathrm{\text{K}})$ samples. With decreasing temperature, the resistivity of the optimally-doped samples has been found to transit from the regime of scattering on phonons and defects to the regime of “semiconductor” character and, near $T_c$, of the fluctuation conductivity. The oxygen-poor samples have been revealed to exhibit only a variable range hopping conductivity of “semiconductor” character, which near $T_c$ transits into the fluctuation conductivity. A significant anisotropy of the residual resistivity and characteristics of the fluctuation conductivity is observed for samples of both types.

First-principles calculations were used to investigate the stability, electronic structure, elastic and lattice thermal conductivity of FeS and FeS₂ polymorphs ($\alpha$-FeS, $\beta$-FeS, $\gamma$-FeS, $\alpha$-FeS₂, $\beta$-FeS₂). The calculated lattice parameters were in agreement with experimental results. The results showed that these Fe-S binary compounds are thermodynamically and mechanically stable. The elastic anisotropies of Fe-S binary compounds were exhibited by 3D modulus ball and 2D projections. Among all the five compounds, $\alpha$-FeS₂ compound has the largest bulk modulus and $\beta$-FeS₂ has the largest Young’s modulus and hardness. Furthermore, $\alpha$-FeS, $\beta$-FeS and $\gamma$-FeS compounds can be regarded as ductile material according to $B/G$ and Poisson’s ratio. The FeS compounds show metallic character and FeS₂ compounds show semiconductor character through analyzing their bandgap and density of states (DOS). The $\beta$-FeS₂ has the largest thermal conductivity according to the Clarke model, and the $\beta$-FeS shows the strongest thermal conductivity anisotropy among the five compounds.

The use of conjugated polymers such as poly(3-hexylthiophene) (P3HT) in the active layers of plastic electronic devices could provide a more practical and accessible form of energy production and storage. The efficiency of these devices is intimately connected to the morphology of the polymer chains in the active layer materials, as polymer folding affects mesoscale material morphology. The latter in turn influences electronic structure and thus performance of the active layer. It is, however, highly challenging to determine molecular structure and folding properties in a bulk material. Here, it is shown that through the use of nanoparticles as a model system for the bulk material insight in molecular morphology can be gained through single particle fluorescence excitation spectroscopy. The study of P3HT chain morphologies was accomplished through the investigation of neat (0 wt% PCBM) P3HT nanoparticles and 25, 50 and 75 wt% PCBM blended P3HT nanoparticles. A striking discontinuous trend in P3HT chain morphology as a function of PCBM blending ratio was observed, where P3HT morphologies at 25 wt% and 75 wt% blending ratios appear to be more disordered than those observed for the 50 wt% blending ratio. These data suggest that at least from the morphological perspective, the 1:1 blending ratio appears to yield the better P3HT chain alignment.

Special Issue Comment: This paper about solving single molecule conformations is related to the papers in this Special Issue on mathematical models for treatment of single molecule trajectories,¹ nonblinking inorganic nanocrystals,² and hybrid quantom dot–fullerence composite nanoparticles.³