Reorientation Effect Research Articles

Spin reorientation effect on magnetization - application to Nd2Fe14B

Spin reorientation is a phenomenon observed frequently in magnetic materials and is responsible for changes in magnetization as a function of temperature. In this study an analytical model is described which accounts for such changes in magnetization. Three different magnetization vs. temperature measurements are described which confirm the occurence of spin reorientation and indicate the exact temperature at which it occurs (application to Nd2Fe14B intermetallic compound). The analytical solution of the model enables one to determine the K1/K2 ratio of the first- (K1) and second-order (K2) anisotropy constants as a function of temperature. Also, this model clearly demonstrates the effect of crystal orientation (angle between the c-axis and the applied magnetic field) on the magnetization vs. temperature behavior; one can take advantage of this in order to achieve a maximum or a minimum effect. The effect of the presence of the third-order (K3) anisotropy constant is also discussed.

Electric quadrupole moments of the first excited states of 130,134,138Ba

The static electric quadrupole moments Q(2 1 +) of the first excited states of 138,134,130Ba and the reduced transition probabilities B( E2; O 1 +→ 2 1 +) have been measured using the reorientation effect in Coulomb excitation. It is found for 138Ba that Q(2 1 +) = −0.14 (7) [0.08 (7)] e · b, where in this and the following cases the unbracketed value corresponds to constructive interference from the 2 2 + state and the bracketed value corresponds to destructive interference; for 134Ba Q(2 1 +) = −0.32 (6) [0.09 (6)] e · b for P 3(4 1 +) < 0 or Q(2 1 +) = −0.20 (6) [0.21 (6)] e · b for P 3(4 1 +) > 0; for 130Ba if it is assumed that the mixing ratio δ(E2/M1; 2 2 +→2 1 +) > 1 then Q(2 1 +) = -1.02 (15) [−0.09 (15) ] e · b. Results obtained for B(E2; O 1 +→ 2 1 +) are 0.241 (6) e 2 · b 2, 0.655 (6) e 2 · b 2 and 1.167(11)[1.159 (12)] e 2 · b 2 for 138,134,130 Ba respectively. The results are compared with previous measurements and with the predictions of various nuclear models.

Quadrupole moment of the first 2(+) excited state in 64Zn.

The Coulomb excitation probability of the first ${2}^{+}$ state of $^{64}\mathrm{Zn}$ was measured observing the backscattered ions of $^{4}\mathrm{He}$, $^{16}\mathrm{O}$, and $^{18}\mathrm{O}$. The static and the reduced transition probability B(E2;${O}^{+}$\ensuremath{\rightarrow}${2}^{+}$) have been determined using the reorientation effect. It is found that =-0.32\ifmmode\pm\else\textpm\fi{}0.06 e b (-0.26\ifmmode\pm\else\textpm\fi{}0.06 e b) for constructive (destructive) interference involving the second ${2}^{+}$ state, and that B(E2;${O}^{+}$\ensuremath{\rightarrow}${2}^{+}$) =0.168\ifmmode\pm\else\textpm\fi{}0.004${\mathrm{e}}^{2}$${\mathrm{b}}^{2}$, for both cases.

Adsorption of α-, ⨿- and γ-cyclodextrins on mercury electrodes from 1 M NaC1O 4 and 0.5 M Na 2SO 4 aqueous solutions

The adsorption of α-, ⨿- and γ-cyclodextrins on mercury electrodes from l M NaClO 4 and 0.5 M Na 2SO 4 was investigated, using surface tension and differential capacity measurements. All three cyclodextrins adsorb on mercury and, in addition, α- and γ-cyclodextrins exhibit a behaviour typical of the two-dimensional condensation of organic adsorbates in both electrolytes. They also show strong reorientation effects in the adsorbed state. A comparison of possible models of electrode occupation by surfactant molecules with the experimentally determined surface excesses shows that at less negative potentials the molecules of cyclodextrins are oriented with the cavity perpendicular to the electrode surface, while at more negative potentials an orientation intermediate between the “parallel” and “perpendicular” prevails.

Orientational effects in Langmuir films of poly(γ-benzyl-L-glutamate) studied by polarised infrared spectroscopy

Langmuir films of poly( gamma -benzyl-L-glutamate) (molecular weight=28000) at a variety of surface pressures both below and above the monolayer-bilayer transition have been deposited onto infrared-transparent chalcogenide glass discs using a horizontal touching method. Polarised infrared spectra were obtained on the resultant films (about 60 monolayers thick) and the dichroic ratios of the four strongest absorptions (3292, 1733, 1655 and 1549 cm-1) were measured. At very low pressures (2.5 mN m-1) the alpha -helices in the monolayer are randomly orientated. At moderate pressures (5-10 mN m-1) where the film is a monolayer, the helices are oriented predominantly perpendicularly to the compressing barrier, but in a collapsed bilayer (25 mN m-1) they are predominantly parallel to the barrier. The results, which are not confused by the direction of withdrawal as in conventional Langmuir-Blodgett deposition, demonstrate clearly an interesting reorientation effect in these films.

Non adiabatic theory of collisions in a radiative field. Semi-classical limit

The quantal theory of atomic collisions in a radiative field is now well established for weak fields which we consider here. Several calculations of radiative cross sections and redistribution of polarization compare extremely well with experimental results. Semi-classical approaches often allow a better physical interpretation. However, the above mentioned results show that trajectory and internuclear reorientation effects during the collision play an essential role so that sophisticated methods have to be developed. In this paper (paper 1), we derive the semi-classical close coupled equations in the limit of large quantum numbers of the quantal equations thereby avoiding the rectilinear trajectory assumption. An adequate choice of the axis frame of reference allows us to show the exact correspondence between this approach and the direct semi-classical derivation of the close coupled equations. This leads us to interpret physically the P, Q, R spectroscopic branches in terms of the rotation of the internuclear axis during the collision Obtention des equations couplees semi-classiques et des sections efficaces radiatives comme limites, aux grands moments cinetiques, des expressions quantiques correspondantes, ce qui permet de s'affranchir d'une hypothese de trajectoire rectiligne. Par un choix adequat des systemes d'axes, etablissement d'une correspondance exacte avec l'approche semi-classique directe. Interpretation physique des branches spectroscopiques P, Q, R en termes de rotation de l'axe internucleaire durant la collision

Polarisation optical bistability in nematic liquid crystals

The first demonstration of high contrast polarisation bistability due to thermally induced cavity and reorientational effects is reported. A novel configuration for bistable polarisation switches in a birefringent nonlinear cavity is also demonstrated and described theoretically.

High-frequency librational solvent reorientation and nonlocal dielectric solvent effects in optical intervalence transitions

High-frequency librational solvent reorientation and nonlocal dielectric solvent effects in optical intervalence transitions

Ground state reorientation effects in elastic scattering cross sections

Elastic scattering cross sections are shown to be quite sensitive to ground state reorientation amplitudes and cross sections. These effects are dramatically evident when comparing scattering from even-even nuclei with that from high-spin odd- A nuclei, and may affect choices of potentials for odd versus even nuclei. Neutron scattering data from 235U and 238U are analyzed via coupled channels methods. The diffraction minima in elastic scattering from 235U are found to be dominated by reorientation cross sections. The majority of this reorientation is shown to follow from second order virtual nuclear excitations rather than proceeding through amplitudes for direct ground state reorientation.

Reorientation effects for 52 MeV vector polarized deuterons

The differential cross sections, dσ(θ) dΩ , and the vector analysing powers, iT 11( θ), were measured for the elastic and inelastic scattering of 52 MeV vector polarized douterons from 20Ne, 22Ne, 26Mg, 28Si, 32S, 34S, 36Ar and 40Ar nuclei. Coupled channels analysis was carried out using an axially symmetric rotational model with either prolate or oblate quadrupole deformations for each isotope. Calculations assuming harmonic vibrator model were also carried out. In general, reorientation effects were found to be weak. A global optical model potential containing an imaginary spin-orbit component was found to be the most suitable in describing the experimental data at this energy.

ChemInform Abstract: Benzene Adsorbed on Silver: An Electron Energy Loss and Surface‐Enhanced Raman Study.

Vibrational electron energy loss (EELS) and surface‐enhanced Raman (SERS) spectra of benzene on evaporated silver display marked coverage dependence for ‘‘cold‐deposited’’ surfaces prepared at or above 150 K. In contrast, silver deposition at 60 K leads to less complex behavior. On ‘‘warm’’ prepared surfaces, 150–300 K, there exists a low coverage spectrum and a distinctly different high coverage (still submonolayer) spectrum. On cold prepared surfaces, 60 K, only one type of spectrum appears and it closely resembles the high coverage spectrum seen on a warm prepared surface. The dependence on silver preparation temperature, evidence that different sites lead to different spectra, and the expectation that benzene forms substantial π bonds only, implies that this is not a compressional reorientation effect like that observed previously for pyridine on Ag(111). It appears that cold prepared surfaces have very rough features giving rise to only one type of spectrum, while warm prepared surfaces have smooth a...

Relation between structure and mechanical behaviour of fibre-reinforced composite materials at large strains

A theory is presented for the mechanical behaviour of fibre-reinforced composite materials at large strains. It is based on the distribution of fibres within the material and uses only basic mechanical properties of the fibres and matrix. The angular distribution of fibres is described by an orientation distribution function, g ( θ, ϕ ), which changes as the material is stretched, becoming greater along the directions of greatest tensile strain. No assumption is made about stress transfer to the fibres, or their length, except that they are long enough for this to happen effectively. The analysis predicts the reorientation of the fibres with strain and shows good agreement with preliminary experimental results from spinal ligaments. The predicted stress-strain behaviour shows qualitative agreement with experiment but further analysis is needed to take account of the crimping of the collagen fibres which occurs in this material. The theory may also have application to reorientation effects observed in drawn polymers and this is demonstrated with reference to polyethylene and polyethylene terephthalate.

Quadrupole moment of the first excited state of 136Ba.

The static electric quadrupole moment Q${(2}_{1}^{+}$) of the first excited state of $^{136}\mathrm{Ba}$ and the reduced transition probability B(E${2;0}_{1}^{+}$\ensuremath{\rightarrow}${2}_{1}^{+}$) have been measured using the reorientation effect in Coulomb excitation. It is found that Q${(2}_{1}^{+}$)=-0.19\ifmmode\pm\else\textpm\fi{}0.06 (+0.07\ifmmode\pm\else\textpm\fi{}0.07) e b and B(E${2;0}_{1}^{+}$\ensuremath{\rightarrow}${2}_{1}^{+}$) =0.419\ifmmode\pm\else\textpm\fi{}0.004 (0.417\ifmmode\pm\else\textpm\fi{}0.004) ${e}^{2}$${\mathrm{b}}^{2}$ for constructive (destructive) interference involving the second ${2}^{+}$ state. These results agree well with one of the previous measurements of these quantities, but disagree markedly with another which is of similar precision to the present work.

Benzene adsorbed on silver: An electron energy loss and surface-enhanced Raman study

Vibrational electron energy loss (EELS) and surface-enhanced Raman (SERS) spectra of benzene on evaporated silver display marked coverage dependence for ‘‘cold-deposited’’ surfaces prepared at or above 150 K. In contrast, silver deposition at 60 K leads to less complex behavior. On ‘‘warm’’ prepared surfaces, 150–300 K, there exists a low coverage spectrum and a distinctly different high coverage (still submonolayer) spectrum. On cold prepared surfaces, 60 K, only one type of spectrum appears and it closely resembles the high coverage spectrum seen on a warm prepared surface. The dependence on silver preparation temperature, evidence that different sites lead to different spectra, and the expectation that benzene forms substantial π bonds only, implies that this is not a compressional reorientation effect like that observed previously for pyridine on Ag(111). It appears that cold prepared surfaces have very rough features giving rise to only one type of spectrum, while warm prepared surfaces have smooth and rough areas resulting in the low and high coverage spectra, respectively. The low and high coverage spectra may be an indication that the two types of site support unique orientations. Since however, orientation alone does not account for all observed features it may be that the rough silver surface provides a degeneracy lifting mechanism, possibly a field gradient effect like that proposed in relation to SERS.

Interpretation of the fluorescence decay of 1-methylindole in polar solvents by reorientational effects

Interpretation of the fluorescence decay of 1-methylindole in polar solvents by reorientational effects

Quadrupole moment of the first2+excited state inBa136through the reorientation effect

Measurements of the Coulomb excitation probability of the first ${2}^{+}$ state of $^{136}\mathrm{Ba}$ were carried out using back-scattered ions of $^{4}\mathrm{He}$ and $^{16}\mathrm{O}$. The static quadrupole moment ${Q}_{{2}^{+}}$ and the reduced transition probability $B(E2;{0}^{+}\ensuremath{\rightarrow}{2}^{+})$ have been determined using the reorientation effect. It is found that ${Q}_{{2}^{+}}=+0.01\ifmmode\pm\else\textpm\fi{}0.05e\mathrm{b} (+0.25\ifmmode\pm\else\textpm\fi{}0.05e\mathrm{b})$ for the positive (negative) sign of the ${2}^{+}$\ensuremath{'} interference term, and $B(E2;{0}^{+}\ensuremath{\rightarrow}{2}^{+})=0.399\ifmmode\pm\else\textpm\fi{}0.003{e}^{2}{\mathrm{b}}^{2}$.

An experimental verification of the validity of the reorientation-effect technique for the determination of nuclear quadrupole moments

The static electric quadrupole moment of the ground state of 7Li has been determined using the reorientation effect in Coulomb excitation. The result obtained (−4.0 ± 1.1 e fm 2) is in excellent agreement with values reported from standard techniques and thus provides a strong verification of the validity of the reorientation-effect technique for the determination of nuclear quadrupole moments.

Effects of Time and Perceptual Orientation on Actors' and Observers' Attributions

The actor/observer effect was examined by Storms in a 1973 study which manipulated perceptual orientation using video recordings. Storms' study was complex and some of his results equivocal. The present study attempted to recreate the perceptual reorientation effect using a simplified experimental design and an initial difference between actors and observers which was the reverse of the original effect. Female undergraduates performed a motor co-ordination task as actors while watched by observers. Each person made attributions for the actor's behaviour before and after watching a video recording of the performance. For a control group the video recording was of an unrelated variety show excerpt. Actors' initial attributions were less situational than observers'. Both actors and observers became more situational after the video replay but this effect occurred in both experimental and control groups. It was suggested the passage of time between first and second recording of attributions could account for the findings and care should be taken when interpreting Storms' (1973) study and others which did not adequately control for temporal effects.

Coulomb Excitation of 7Li

Coulomb excitation of the 0�478 MeV, J1t = t-, first excited state of 7Li has been studied using beams of 7Li ions and targets of 138Ba and 208Pb. Spectra of the scattered particles were measured at 171� using an annular Si surface-barrier detector (l 38Ba and 208Pb targets) and at 90� using an Enge split-pole magnetic spectrometer (208Pb targets). For each experimental configuration, the bombarding energy at which nuclear interference became significant was determined experimentally. An analysis based upon the reorientation effect yielded the following results: the static electric quadrupole moment of the J1t = t- ground state (Q3/2-) is -4�0� 1�1 efm", the contribution of the giant dipole resonance (GDR) to the Coulomb-excitation cross section is 2�7 �0�2 times as great as would be calculated from the hydrodynamic model, and B(E2;t-~t-) is 7�42�0�14e2fm4 ? The value obtained for Q3/2- is in excellent agreement with results reported from atomic- and molecular-beam spectroscopy and from Coulomb scattering of aligned 7Li. Thus it provides a strong verification of the validity of the reorientation-effect technique for the determination of nuclear quadrupole moments, provided that the GDR effect is treated adequately.

Quadrupole moment of the first excited state of 32S

The static quadrupole moment and B(E2; 0 + → 2 +) value for the first excited state of 32S were measured using the reorientation effect in Coulomb excitation of 32S projectiles. Silicon surface barrier detectors were used to detect 32S ions scattered from 208Pb at mean laboratory angles of 90° and 174°, for bombarding energies in the range 122 to 160 MeV. The results for constructive (destructive) interference from the second 2 + state in 32S are QP 2 + = −16.0±2.2 (−13.3±2.2) e·fd 2 and B(E2; 0 + → 2 +) = 292±17 (307±17) e 2·fm 4