Dependence Of Anisotropies Research Articles

Structure and magnetic anisotropies in sputtered FePd(1 1 0) thin films

The growth temperature dependence of structure and magnetic anisotropies is studied for epitaxial FePd(1 1 0) alloys grown by sputtering. Partial chemical order is obtained for growth temperatures of 600°C and above. Strong in-plane uniaxial magnetic anisotropy is found for chemically disordered samples grown at 500°C, with a reduction in the anisotropy constants for samples grown at higher temperatures. The obtained anisotropy values can be interpreted as the result of the competition between magnetocrystalline and magnetoelastic anisotropy.

Heavy-ion induced fission fragment angular distributions at near-barrier energies

Heavy-ion induced fission fragment angular distribution measurements performed in recent years have provided interesting results. From a systematic study involving several projectiles and actinide targets, the entrance channel mass asymmetry dependence of fission anisotropies has been brought out at energies above the fusion barrier. It has been observed that the fission fragment anisotropies, essentially for all target - projectile combinations involving actinide targets increase as bombarding energy is lowered below the barrier and are anomalously large when compared to the saddle-point model expectations. However, similar measurements carried out for spherical targets are consistent with the calculations based on the saddle-point model.

The dependence of friction anisotropies on themolecular organisation of LB films as observed by AFM

We performed lateral force microscopy on thiolipid Langmuir-Blodgett (LB) films physisorbed on mica substrates with asilicon tip of an atomic force microscope. The structure ofcondensed domains, reflecting their symmetric morphology, wasobserved. The lateral (friction) forces were measured as a function of (normal) applied load, of sliding velocity and of themolecular orientation of these films. We found that at a fixedvelocity, lateral force increases with applied load in a linearfashion. Within the velocity range 0.01 to~50μm/s, the lateral force signal initiallyincreases monotonically with velocity (static regime) and thenstabilises when the tip begins sliding. The friction force andthe observed asymmetry in the quasi-static ``friction-loops''(torsion of the tip during a forward/reverse scan) were foundto be dependent on the domain orientation with respect to the scan direction, while the measured adhesive force remainedconstant. Together, friction and asymmetry reveal and mapmolecular packing and tilt.

Disappearance of entrance channel dependence of fission fragment anisotropies at well-above-barrier energies.

Fission fragment anisotropies have been measured to energies extending well above the barrier for three entrance channels leading to the same compound nucleus $^{248}\mathrm{Cf}$. For the $^{12}\mathrm{C}$ + $^{236}\mathrm{U}$ and $^{16}\mathrm{O}$ + $^{232}\mathrm{Th}$ systems, lying on either side of the Businaro-Gallone critical asymmetry, the mean square angular momentum is matched at an excitation energy of 62 MeV. The anisotropies, although different at lower energies, are in agreement within experimental errors at this excitation energy and thus show no entrance channel dependence.

Cosmic Microwave Background Anisotropies from the Rees-Sciama Effect in Omega 0 <=1 Universes

We investigate the imprint of nonlinear matter condensations on the Cosmic Microwave Background (CMB) in $\Omega_{0}<1$ cold dark matter (CDM) model universes. We consider simulation domains ranging from $120h^{-1}$ Mpc to $360h^{-1}$ Mpc in size. We concentrate on the secondary temperature anisotropies induced by time varying gravitational potentials occurring after decoupling. Specifically, we investigate the importance of the Rees-Sciama effect due to: (1) intrinsic changes in the gravitational potential of forming, nonlinear structures, (2) proper motion of nonlinear structures, and (3) late time decay of gravitational potential perturbations in open universes. CMB temperature anisotropies are obtained by numerically evolving matter inhomogeneities and CMB photons from an early, linear epoch ($z=100$) to the present, nonlinear epoch $(z=0)$. We test the dependence and relative importance of these secondary temperature anisotropies as a function of the scale of the underlying matter (voids, superclusters) and as a function of $\Omega_{0}$. The results of the $\Omega_{0}<1$ models are compared to a similarly executed $\Omega_{0}=1.0$ simulation. We find that in low density models all three sources of anisotropy could be relevant and reach levels of $\Delta T/T \sim 10^{-6}$. In particular, we find that for $\Omega_{0}<1$ at large scales, secondary temperature anisotropies are dominated by the decaying potential.

Well-width dependence of the optical anisotropies in (001) and (110) semiconductor quantum wells: The effect of spin-orbit split-off bands.

We have investigated both theoretically and experimentally the well-width dependence of the polarization anisotropies of the interband transitions in semiconductor quantum wells (QW's). In our theoretical study, we adopted the six-band Luttinger-Kohn model in which the spin-orbit split-off (SO) bands are included. The polarization-dependent optical-matrix elements at the Brillouin-zone center in (001) and (110) QW's were calculated as a function of the well width using the exact solutions of coupled effective-mass equations. The calculated results are shown for GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As and ${\mathrm{Ga}}_{0.5}$${\mathrm{In}}_{0.5}$P/(${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${)}_{0.5}$${\mathrm{In}}_{0.5}$P (001)-oriented QW's as well as GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As (110)-oriented QW's. In the (001) QW's, the inclusion of the SO bands into the calculation led to a decrease in the TM/TE ratio of the optical-matrix element for the light-hole transition with decreasing well width. In the ${\mathrm{Ga}}_{0.5}$${\mathrm{In}}_{0.5}$P/(${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${)}_{0.5}$${\mathrm{In}}_{0.5}$P system, which has a smaller spin-orbit splitting energy, the decrease in the TM/TE ratio was shown to be more remarkable to show reversal between the TM and TE strength when the hole confinement energy is large.In the (110) QW's, the effect of coupling to the SO bands was revealed to appear not only for the light-hole transition but also for the heavy-hole transition. The calculated results for (110) GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As QW's illustrated that the anisotropy regarding the polarization direction in the (110) QW plane increases with decreasing well width according to the increase in coupling to the SO bands. In order to investigate experimentally the well-width dependence of the in-plane optical anisotropy in (110) QW's, polarized photoluminescence measurements were performed at 77 K on (110) GaAs/${\mathrm{Al}}_{0.2}$${\mathrm{Ga}}_{0.8}$As QW structures having various well widths. The in-plane anisotropy of heavy-hole excitonic emission was observed to be almost unchanged for well widths wider than 9 nm, while it was observed to increase for narrower well widths with decreasing well width. The degree of linear polarization observed in the photoluminescence measurements showed good agreement with the calculated results.

Preequilibrium fission for low angular momentum

We have compared the fragment anisotropies of 11B + 237Np and 16O + 232Th which both populate the same fissioning system 248Cf. The data clearly show the evidence of the entrance-channel dependence of fission-fragment anisotropies. A new version of the preequilibrium fission model is put forward. In the framework of this model, the discrepancy between the experimental mean-square angular momentum 〈 J 2〉 exp. and the prediction of the coupled-channels model, 〈 J 2〉 theory is reasonably removed.

Mass resolved angular distribution in 10B, 12C, and 16O induced fission of 232Th.

The recoil catcher technique and gamma spectrometric assay of fission products were used to measure angular distribution of 17 fission products in $^{10}\mathrm{B}$, $^{12}\mathrm{C}$, and $^{16}\mathrm{O}$ induced fission of $^{232}\mathrm{Th}$ at near barrier energies. The observed mass dependence of anisotropies of fission products in these systems are very different from that of p and \ensuremath{\alpha} induced fission of $^{232}\mathrm{Th}$ at similar excitation energies. It has been suggested that the difference in the rotational energy for the symmetric and asymmetric modes for large compound nucleus spins could be responsible for the observed variation. No systematic change in the mass dependence of anisotropies across the Bussinaro-Gallone point was observed. For $^{16}\mathrm{O}$ induced fission of $^{232}\mathrm{Th}$, sharp variation in anisotropies have been observed in the mass region 120--135. This has been attributed to transfer induced fission.

Effects of structural phase transitions on Superconductivity and magnetism in substituted derivatives of La 2CuO 4

Structural (neutron and x-ray diffraction) and magnetic (neutron diffraction and magnetic susceptibility) measurements of materials derived from La 2CuO 4 by isovalent and aliovalent substitution in the La 3+ site have been performed. Such substitutions permit the tilts of the CuO 6 octahedra (about the (110) and (1 10) axes of the undistorted 14/mmm structure), and the hole concentration in the CuO layers, to be independently varied. The results of these measurements, in combination with those from other research groups, demonstrate that all four tilt structures, HTT (high temperature tetragonal, 14/mmm), LTO1 (low temperature orthorhombic 1, Bmab), LTO2 (low temperature orthorhombic 2, Pccn) and LTT (low temperature tetragonal, P4 2/ncm), support bulk superconductivity, with T c ( HTT) > T c ( LTO1) > T c ( LTO2) > T c ( LTT) at the same hole concentration. Furthermore, there is a strong suppression of superconductivity when the doped carrier concentration is 1/8 hole per Cu 2+ in the LTT and LTO2 phases of these materials. The reason for this T c suppression is not established. Finally, the magnetic structures adopted by the Cu 2+ spins in the insulating phases, determined by neutron diffraction, are also influenced by the tilts of the octahedra. This may reflect a structural dependence of interlayer and intralayer magnetic anisotropies.

A two-fluid approximation for calculating the cosmic microwave background anisotropies

view Abstract Citations (91) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Two-Fluid Approximation for Calculating the Cosmic Microwave Background Anisotropies Seljak, Uros Abstract We present a simple, yet accurate approximation for calculating the cosmic microwave background anisotropy power spectrum in adiabatic models. It consists of solving for the evolution of a two-fluid model until the epoch of recombination and then integrating over the sources to obtain the CMB anisotropy power spectrum. The approximation is useful both for a physical understanding of CMB anisotropies, as well as for a quantitative analysis of cosmological models. Comparison with exact calculations shows that the accuracy is typically better than 20 percent over a large range of angles and cosmological models, including those with curvature and cosmological constant. Using this approximation we investigate the dependence of the CMB anisotropies on the cosmological parameters. We identify six dimensionless parameters that uniquely determine the anisotropy power spectrum within our approximation. CMB experiments on different angular scales could in principle provide information on all these parameters. In particular, mapping of the Doppler peaks would allow an independent determination of baryon mass density, matter mass density and Hubble constant. Publication: The Astrophysical Journal Pub Date: November 1994 DOI: 10.1086/187601 arXiv: arXiv:astro-ph/9406050 Bibcode: 1994ApJ...435L..87S Keywords: Anisotropy; Background Radiation; Baryons; Cosmic Rays; Cosmology; Microwaves; Power Spectra; Two Fluid Models; Adiabatic Equations; Approximation; Astronomical Models; Density (Mass/Volume); Evolution (Development); Microwave Spectra; Recombination Reactions; Stellar Radiation; Astrophysics; COSMOLOGY: THEORY; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; Astrophysics E-Print: 12 pages, AAS Latex, ApJL, submitted 1994, preprint MIT-CSR-94-13 full text sources arXiv | ADS |

Magnetic anisotropies of ultrathin Co films on Cu(1 1 13) substrates.

All magnetic anisotropy contributions in single-crystalline (1 1 13)-oriented Co films on Cu were determined at room temperature using Brillouin light scattering. An in-plane uniaxial anisotropy contribution, not found in the reference system Co/Cu(001), is identified as magnetoelastic in origin. From the thickness dependence of the in-plane anisotropies of both twofold and fourfold symmetry about the film normal it is concluded that elastic strain fields are very likely to provide the driving mechanism for stabilizing ferromagnetic order in ultrathin Co(1 1 13) films.

Low-temperature nuclear orientation of CeNi 2Al 5 and CeNiSn

Hyperfine interactions at Ce sites of CeNi 2Al 5 and CeNiSn single crystals were investigated by means of the low-temperature nuclear orientation of the 141Ce isotope. From the temperature dependence of γ-ray anisotropies the hyperfine fields at Ce nuclei in CeNi 2Al 5 and CeNiSn were deduced as 92 (±6) T and <6 T, respectively.

Thickness and temperature dependence of magnetic anisotropies in ultrathin fcc Co(001) structures.

Metastable fcc Co(001) structures were grown on fcc Cu(001) using molecular beam epitaxy. Magnetic properties of these structures were studied using the ferromagnetic resonance technique. The uniaxial perpendicular and fourfold in-plane anisotropies are presented for different thicknesses. Both anisotropies are shown to be well described by a sum of contributions from the constant volume term and the 1/d-dependent surface term. The effect of tetragonal distortion on magnetic anisotropies is presented. The temperature dependence of anisotropies is discussed.

On-line orientation of bromine isotopes

Assignments for the principal Nilsson configuration in light β+-decaying bromine isotopes were proposed in a contribution to the OLNO-1 conference. These assignments were made on the basis of magnetic moments derived from the temperature dependence of anisotropies in daughter Se isotopes observed in the DOLIS-COLD facility at Daresbury. Anisotropy measurements have since been extended to a lower base temperature in74mBr and72gBr decay, leading to more stringent limits on the ground state moment of72Br. The proposed π[312]3/2 configuration for75Br has also now been confirmed by a measurement of the sign of its magnetic moment. This was done by observing the β-asymmetry in75Br decay using high purity Si detectors mounted within the dilution refrigerator.

Fission fragment angular distributions for the system 19F+232Th.

The fission fragment angular distributions for the system $^{19}\mathrm{F}$${+}^{232}$Th have been measured at several bombarding energies between 94 and 108 MeV. Even though the anisotropy values measured in the present work are considerably smaller than the ones reported by Zhang et al. for the same system at similar energies, they are still anomalous when compared with the predictions of the standard saddle-point statistical model and fit into the systematics of entrance-channel dependence of fission anisotropies reported by us earlier.

Magnetic properties of amorphous NdFeB thin films

Transverse biased initial susceptibility (TBIS) measurements have been performed in as-prepared and in UHV annealed NdFeB and FeB amorphous films. The dependence of magnetic anisotropies (local and macroscopic) on substrate temperature during deposition ( T s = RT and 77 K) and subsequent annealing treatments is discussed.

Principle of Corresponding States of Magnetic Phase Diagram of CuCl2·2H2ZO at Low Temperatures and High Pressures

The principle of corresponding states of the magnetic phase diagram of CuCl2·2H2O (TN=4.35K) at low-temperatures, hydrostatic pressures and magnetic fields has been studied by the low-temperature heat capacity measurements. The Néel temperature TN(p) has changed linearly with pressure p(kbar) as TN(p)=TN(0)(1+0.048p) up to 6 kbar at zero external field. The dependence of magnetic interactions on pressure (or inter-ion distance) is revealed to give the larger value of the magnetic Grüneisen constant than expected for the superexchange mechanism. The phase boundary between paramagnetic and antiferromagnetic phases has been examined at high hydrostatic pressures and magnetic fields applied along the spin easy axis. The principle of corresponding states of the magnetic phase diagram of this compound has been checked by a molecular field approximation in the consideration of the pressure dependence of magnetic interactions and anisotropies.

Tensor representation of Oseen-Frank strain energy in uniaxial cholesterics

de Gennes gave a three-parameter representation of strain energy in a cholesteric liquid crystal that is second order on the $Q$ tensor, and hence in order parameter. He discarded a term involving an elastic constant ${K}_{24}$ which is relevant at surfaces and disclinations. The splay and bend elastic constants ${K}_{11}$ and ${K}_{33}$ are alike in the second-order theory. The complete Oseen-Frank expression in terms of a director has five parameters, including ${K}_{24}$. If uniaxiality, which is implicit in the director theory, is imposed on the $Q$ tensor, five independent third-order tensor functions are found. These differentiate between ${K}_{11}$ and ${K}_{33}$ and show the third-order dependence of the Oseen-Frank elastic constants on order parameter. Numerical values of these second- and third-order elastic coefficients of 4-methoxybenzylidene-4\ensuremath{'}-$n$-butylaniline (MBBA), $p$-azoxyanisole (PAA), and E-7 (British Drug House designation of a cyano-biphenyl mixture) are obtained from published values of the dependence of Oseen-Frank elastic constants and various anisotropies on temperature, and from a relation of Nehring and Saupe.

Transition-State Theory for Fission Angular Distributions: A Flexible-Rotor Model

Current studies of heavy-ion reactions make extensive use of fission-fragment angular distributions to prove the limits of statistical equilibrium. The "standard" theory was derived for a rigid-rotor, transition-state nucleus. Here a more complete theory is developed by inclusion of the dependence of transition-state shape on orientation of the symmetry axis. It is concluded that even this improved application of the liquid-drop model cannot give an adequate prediction of the $\frac{{Z}^{2}}{A}$ dependence of fission-fragment anisotropies.

Temperature dependence of creep-induced and field-induced anisotropy in a zero magnetostriction amorphous alloy

The creep-induced anisotropy Kc, the field-induced anisotropy Kf, and the saturation magnetization Ms have been measured from 77 to 300 K on a zero-magnetostriction cobalt-based amorphous alloy. The temperature dependence of both anisotropies can be expressed as K=kMn, with n=2.6±0.1. Since both anisotropies have the same temperature dependence, they presumably have the same structural origin, namely anelastic structural defects or shearable components, even though they are different in magnitude by a factor of 10.