Anisotropy of the 15 eV volume plasmon dispersion in A1

A dependence of plasmon dispersion for epitaxial aluminum films has been found for the directions [100], [110] and [111]. A differene of about 0.5 eV has been observed between the directions [100] and [110] at q = 1.4 Å^?1. This effect is due to the influence of lattice on the electron gas.     

Lattice dynamics of a Pd0.90Rh0.10 crystal

Using inelastic neutron scattering, the phonon dispersion relations along the [100], [110] and [111] directions of a single crystal of Pd_0.90Rh_0.10 have been measured at 296K. From these results and phonon data for Pd, the phonon frequency shifts,(q), and the self-energy function, _j (q, _j (q)), have been determined for all branches. The frequency changes exhibit large wave vector and polarization dependence and behave non linearly with the increase concentration of Rh. The seventh neighbour tensor Born-von Kármán model has been fitted to the experimental phonon dispersion curves, and the force constants and elastic constants calculated. Correlations between the phonon anomalies, displayed in the slope ofT ₁ [110] branch, and the structure of the generalized susceptibility function, ₀(q), for Pd were discussed. From which follows the influence of the electron-electron interaction on theT ₁ [110] branch in Pd and Pd-Rh alloys.     

Compton profiles and nesting of Fermi surfaces for B2-TiNi and B2-TiPd

The band structures of the shape memory alloys B2-TiNi and B2-TiPd are calculated by the full potential linearized augmented plane wave method with the local density approximation. The theoretical Compton profiles for B2-TiNi and B2-TiPd are calculated. In addition, the three-dimensional (3D) occupation number densities obtained by Lock-Crisp-West (LCW) analysis are presented for the first time. These 3D occupation number densities are in good agreement with the Compton scattering experiment for TiNi. Both shape memory alloys are based on martensitic transformation, which is caused by soft phonons. The charge-density wave is created by nesting of Fermi surfaces, which leads to phonon softening. To examine the nesting vectors quantitatively, we calculate the generalized susceptibility χ(q). χ(q) shows peaks at 0.315[110]2π/a and 0.4[111]2π/a for TiNi and at 0.275[110]2π/a and 0.395[111]2π/a for TiPd. Although the nesting vector in the [110] direction agrees with that from the phonon experiment, the nesting vector in the [111] direction differs from that in the experimental results.     

Experimental proof for a quasi-one-dimensional band structure of V3Si

A positron annihilation experiment on V₃Si in the [100] direction is presented. It shows that the Fermi surface (FS) contains planar sections, proving the q-1-D nature of the electronic band structure. One possible way to account for the positions of the planar sections, is by a band structure with a FS at $\text{～ 0.9}\text{π}\text{a}$, belonging to the σ-band (m_l = 0) and a δ₂-band (m_l = ±2) with a density of states peak just below the Fermi level, which yields planar sections of the FS at $\text{～ 0.2}\text{π}\text{a}$ and $\text{～ 0.6}\text{π}\text{a}$, in agreement with a LCAO calculation.     

Magnetic characteristics of PrCd single crystal

Magnetic measurements have been made along the [100], [110] and [111]-axes of PrCd single crystal in magnetic fields up to 70 kOe in the temperature range from 4.2 to 300 K. PrCd shows metamagnetism below T_t = 25 K in which two critical fields are observed in the magnetization processes along the [110] and [111]-axes and a critical field along the [100]-axis. The metamagnetic behaviour is interpreted by a noncollinear antiferromagnetic model with the Pr moments of ～ 2μ_B directed to the 〈111〉-axes.     

Anisotropy of positron wave function in 4d transition metals

The positron wave functions have been calculated employing the method of expansion of symmetrized plane waves in some 4d transition metals. Systematics of the positron wave functions along the three symmetry directions [100], [110], [111] in these metals, have been discussed. The anisotropies of the ψ₊ have been found to be strongly dependent upon the crystal symmetries. The results of the band structure calculation of 2γ-angular correlation in Rh and Ag are presented.     

Study of the anisotropy of the dielectric response of Na<Subscript>1/2</Subscript>Bi<Subscript>1/2</Subscript>TiO<Subscript>3</Subscript> relaxor ferroelectric

The dielectric response, conductivity, and domain structure of (Na_1/2Bi_1/2)TiO₃ single crystals are studied in the temperature range of 290–750 K for the [100], [110], and [111] crystallographic directions. It is shown that the region of optical isotropization is observed in polarized light in the temperature range of 570–620 K. In this case, the birefringence (Δn) decreases and disappears (together with the image of the domain structure) for the [100] directions. The region of optical isotropization in the [111] directions is characterized by the disappearance of the image of the domain structure and by the existence of individual regions with partial quenching. The domain structure in the [110] directions remains distinguished against the background of a significant decrease in Δn in the indicated temperature range. The region of isotropization is also manifested in the temperature dependence of the imaginary part of the dielectric response and is determined by the isotropic character of the conductivity in the range of 570–620 K. The bulk conductivity has a thermally activated character with activation energies E _a = 50?60 meV at T < 500 K and E _a = 700?900 meV for T > 620 K. The low-frequency dispersion of the dielectric response is determined by the Maxwell–Wagner mechanism and is due to an increase in the ionic conductivity at temperatures above 620 K. The anisotropy of the susceptibility holds in the entire studied ranges of frequencies (25 Hz–1 MHz) and temperatures.     

Stability,elastic properties and electronic structures of L12-ZrAl3 and D022-ZrAl3 up to 40 GPa

The effects of high pressures on structure stability, elastic properties and electronic structures of zirconium trialuminide L1₂- and D0₂₂-ZrAl₃ compounds have been investigated by first-principles calculations within the local density approximation. The equilibrium structure and formation energy show that L1₂-ZrAl₃ is more stable than D0₂₂-ZrAl₃ at the applied pressure. The elastic properties and Debye temperatures of (L1₂, D0₂₂)-ZrAl₃ increase with the increasing pressure and the calculated values in the ground state are in good agreement with the available experiment data. The mechanical anisotropic properties were discussed using the universal anisotropic index A^U. The sound velocities along the [100], [110] and [111] directions were also calculated for both phases. The calculated electronic properties under high pressures suggest that the decreased electronic density of states (DOS) at the Fermi level and the changed charges distribution lead to the observed decrease of the structural stability for (L1₂, D0₂₂)-ZrAl₃ under high pressures.     

Longitudinal relaxation of Fe nuclei in Yb-doped YIG

Measurements of T₁ for ⁵⁷Fe nuclei in Yb-doped YIG are reported for the temperature range 0·7–140 K, with the magnetization along the [111], [100], [110], and [112] crystallographic directions respectively. The dependence of T₁ on Yb concentration and on the magnitude of the applied field was also studied. These results are interpreted in terms of the ‘slow relaxation theory’, and are correlated with the ferrimagnetic resonance work of Clarke, Tweedale, and Teale, whose data have been reanalyzed by us. Both sets of data can be represented fairly well by the theory, with a consistent set of relevant parameters. However, the tensor G which describes the splitting of the Yb ground-state doublet must be modified somewhat from that deduced by Clarke et al., the new principal values being G₁ = 29·0 cm⁻¹, G₂ = 20·4 cm⁻¹ and G₃ = 8·5 cm⁻¹ respectively. Below approximately 10 K, when the magnetization is in the [110] or [112] direction, the nuclear relaxation rate is higher than predicted. These anomalies correspond to those observed in ferrimagnetic resonance line width, which have been attributed to Yb ions on the octahedral lattice sites normally occupied by iron. Anomalously large values of T⁻¹₁ are also observed below approximately 4 K in the [111] and [100] directions, and these remain to be accounted for.     

ESR of adsorbates on single crystal metal surfaces under UHV conditions

Angular dependent electron spin resonance measurements were taken for paramagnetic molecules adsorbed on metallic single crystal surfaces in UHV. For the hydrated Cu(NO₃)₂ complex on a Cu[111] surface an angular dependent ESR signal is recorded. The plane ofthe molecule is found to lie preferentially out of the surface plane. Experiments on chemisorbed molecular O₂ on Ag[110] at 25 K and NO on Pt[111] at 110 K show no sharp ESR signal characteristic for well localized moments. If one assumes that NO on Pt (respectively Pd) carries an unpaired spin, one can estimate a lower limit for the spin flip rate of π^?1>2×10⁹s^?.     

Anisotropy in the angular correlation curves of NiO

The positron angular correlation curves were measured along the [100], [110] and [111] directions of NiO single crystals. A simple calculation based on the localized ion model shows that the measured anisotropy is ascribed to the uncompleted 3d orbitals of Ni with a slight covalent mixing of oxygen 2p orbitals.     

Effects of growth direction on lasing performance in GaAs---AlxGa1−xAs quantum wells

The properties of GaAs---AlGaAs quantum well lasers are studied theoretically as a function of the crystallographic growth direction. The growth directions considered are [001] [111], [110], [310], [311] and [211]. The electronic dispersion is obtained using an 8×8 k·p Hamiltonian which couples the electron, heavy-hole, light-hole and spin-orbit split-off bands. We calculate the threshold current for single quantum well lasers and determine the lowest threshold current for the growth directions considered. It is seen that for some growth directions the threshold current can be less than that previously calculated for a strained-layer quantum well laser. The results also differ from a previous model which completely decoupled the valence and conduction bands.     

[Co/Pd]4–Co–Pd–NiFe spring magnets with highly tunable and uniform magnetization tilt angles

By varying the Pd thickness (t_Pd) from 0 to 8 nm in [Co/Pd]₄/Co/Pd(t_Pd)/NiFe exchange springs, we demonstrate (i) continuous tailoring of the exchange coupling between a [Co/Pd]₄/Co layer with perpendicular anisotropy, and a NiFe layer with an in-plane easy axis, (ii) tuning of the NiFe out-of-plane magnetization angle from 20^○ to 80^○, and (iii) an up to two-fold increase in the NiFe damping. The partial decoupling also results in a highly uniform NiFe magnetization. These properties make [Co/Pd]₄/Co/Pd(t_Pd)/NiFe spring magnets ideal candidates for use as tilted polarizers, by combining stable and well-defined spin directions of its carriers with a high degree of angular freedom.     

Zeeman studies of the 0.839eV emission in SI GaAs:Cr

The multi-structured zero phonon transitions of the 0.839eV emission observed in SI GaAs:Cr have been investigated by Zeeman measurements. Magnetic splittings for the directions [111], [110] and [100] as well as angular dependence studies in the (110) plane show that the centre has a symmetry axis along [111] with a small orthorhombic distortion. The emissions cannot be due to the isolated [100] Jahn-Teller distorted Cr²⁺ ions observed in magnetic resonance but to [111] centres such as the (Cr²⁺-donor) pairs as suggested by White.     

Ab initio investigation on mechanical properties of copper

Employing the ab initio total energy method based on the density functional theory with the generalized gradient approximation, we have investigated the theoretical mechanical properties of copper (Cu) systematically. The theoretical tensile strengths are calculated to be 25.3 GPa, 5.9 GPa, and 37.6 GPa for the fcc Cu single crystal in the [001], [110], and [111] directions, respectively. Among the three directions, the [110] direction is the weakest one due to the occurrence of structure transition at the lower strain and the weakest interaction of atoms between the (110) planes, while the [111] direction is the strongest direction because of the strongest interaction of atoms between the (111) planes. In terms of the elastic constants of Cu single crystal, we also estimate some mechanical quantities of polycrystalline Cu, including bulk modulus B, shear modulus G, Young's modulus E_p, and Poisson's ratio ν.     

Light scattering by electrons in osmium: Effect of pressure

The inelastic electron scattering of light and phonons in single crystals of 5d osmium transition metal has been analyzed at pressures up to 60 GPa and temperatures of 10–300 K. An anomalous increase in the intensity of the spectra of the electron scattering of light with the appearance of pronounced continua at ～580 and 350 cm^?1 for q ‖ [0001] and q ‖ [10\(\overline 1 \)0], respectively, has been observed in a pressure range of 20–30 GPa at an excitation energy of 2.41 eV. The comparison of the q dependences measured and calculated in the framework of the band theory of the spectra implies the significant renormalization of energies and relaxation of electronic states near the Fermi energy and the dependence of the Fermi energy on the pressure and temperature.     

Ni54Fe19Ga27单晶的形状记忆和超弹性

本文研究了单晶Ni₅₄Fe₁₉Ga₂₇不同方向的形状记忆效应、超弹性和磁性. 研究发现,单晶样品具有良好的双向形状记忆效应.不同晶体学方向的相变应变随着热循环次数的变化而改变. 在外应力作用下,通过应力诱发马氏体相变,样品在[001],[110],[111]方向分别产生了3.3%, 2% 和3%的可回复应变平台.磁性测量结果表明马氏体的磁晶各向异性能约为4.8× 10⁵ erg/cm³,远远小于变体孪生所需机械应力能,因此磁场的作用是使磁矩发生转动而不是使孪晶界移动, 成功揭示了不能在NiFeGa中获得大磁感生应变的物理根源.     

The lattice dynamics of SrCl2

Phonon dispersion curves of Sr Cl₂ have been measured at room temperature in the [001], [110] and [111] directions using inelastic neutron scattering. The results are interpreted by means of a polarizable ion model.     

Temperature dependence of the magnetoresistance of single crystal aluminium

The magnetoresistance of single crystal aluminium was measured with the magnetic field in the three main crystallographic directions [100], [110] and [111], in the temperature range 4.2–20 K and in magnetic fields up to 7 T. The exponent of a Tⁿ-law is shown to be decreasing with increasing fields.