M. J. Freiser

On the Measurement of Indices of Refraction of Nematic Liquids

Abstract We wish to report on a simple method for measuring the birefringence and indices of refraction of nematic liquids with an accuracy comparable with or superior to previously reported means.(1–3) The method is exemplified in measurement of the temperature dependences of the indices of refraction of p-methoxybenzylidene p-butylaniline (MBBA) at two wavelengths.

Multiplet Structure in the Absorption Spectrum of Eu2

The Eu2+ ion in alkaline earth fluorides produces two broad absorption bands arising from 4f−5d transitions. The band at 3 eV has a structure with six resolved peaks. This structure is independent of Eu concentration. This band is attributed to transitions from the 4f 7(8 S) ground state to 4f 6(7 FJ ) 5eg , the peaks being associated with the different J values in f 6(7 F). The higher energy band in the fluorides and the absorption band in the europous chalcognides are correspondingly attributed to 4f 6(7 FJ ) 5t 2g states. With this model, with 7 FJ intervals obtained from the resolved structure in the EuF2 data, and from the experimental oscillator strengths of the observed absorption bands, the 4f−5d radial integral is calculated and a consistent set of values of 0.23±0.01 A obtained. The Faraday and Voigt magneto‐optic effects are calculated for EuF2 at 4330 A. The room‐temperature Verdet constant is −7.1 min/Oe·cm as compared with the experimental value of −6.6 min/Oe·cm. The Voigt birefringence at 15°K and 20 kOe is n∥−‐n⊥=−2.0×10−4 while experiment gives −1.7×10−4.

Structural changes in bilayer membranes by multivalent ions

Formation of microlenses, a reduction in thickness, and a change in mechanical properties have been observed when Ca2+ or other multivalent ions are added to bathing solutions of Mueller-Rudin membranes of acidic phospholipids. The observations are interpreted as an extrusion of residual solvent from the hydrocarbon core of the bilayer due to changes in packing imposed by the reduction of electrostatic repulsion of the head groups.

Magnetic Effects on the Optical Absorption of EuO and EuS

The relationship between optical absorption and ferromagnetic order has been investigated on single crystals and thin films of EuO and EuS. The 4f7‐4f65d transition can be identified in evaporated films as an absorption peak of ∼105 cm−1 at 2.1 and 2.4 eV, respectively, which tails out exponentially to lower energies. The onset of the ferromagnetic order is accompanied by an unusually large red shift of the absorption peak which superimposes on the normal magneto optical dichroism. The detailed temperature dependance of this shift does not relate exponentially to the variation in magnetization as found earlier by Busch et al. for powdered samples,1 but is approximately proportional to the nearest neighbor spin correlation function 〈S1S2〉/S2. This is in agreement with an exciton like model for the excited state in which the electron is localized in 5d‐orbitals at the excited Eu‐ion and its 12 nearest Eu neighbors. The exchange interaction of the excited electron with the neighboring 4f7‐spins causes the re...

The Contribution of Rare-Earth Ions to the Anisotropy of Iron Garnets

The low-temperature properties, in iron garnets, of rare-earth ions with an odd number of electrons can be described by a simple model. This model represents the energy levels of the rare-earth ion by an isolated doublet which is subjected to an anisotropic exchange interaction. The complex shapes of the torque curves, predicted by the model and observed at low temperature, are represented by Fourier expansions. A small torque contribution proportional to the applied magnetic field is predicted, and evidence of its existence is observed in (YbY) and (YbGd) iron garnets. A comparison of the behavior of Yb and Dy in YIG and GdIG indicates a moderate influence of the host lattice on Yb and a drastic influence on Dy. The anisotropy anomaly observed for Yb in YIG [at 32° from [001] in the (110) plane] is not present when Yb is substituted into GdIG.

Texturing: A new effect in the dynamic scattering regime of liquid‐crystal cells

A phenomenon observed in homeotropically aligned liquid‐crystal cells after prolonged excitation in dynamic scattering is presented. The phenomenon, because of its visual appearance, is called texturing and is found to be associated with the induction of a metastable configuration in the liquid crystal. A model for the metastable configuration which is consistent with the experimental observations is proposed. Texturing is undesirable in display applications and has been found to occur in matrix‐addressed liquid‐crystal cells.

Antiferromagnetic Resonance in Cubic RbMnF3

Antiferromagnetic resonance has been observed in cubic RbMnF3, and the results are in excellent agreement with a theoretical treatment of the resonance conditions. Because a more detailed publication has recently appeared,1 we present in this abstract a brief background and comments on the observed temperature dependence.Cubic RbMnF3 is characterized by a strong exchange interaction (TN≃54.5°K)2 and low anisotropy. The anisotropy energy has the form EA = K(α4+β4+γ4), where K is positive. When the sublattice magnetization is close to the preferred {111} direction, the anisotropy may be represented by an effective field of 5.0 Oe at 4.2°K. The exchange field is found to be 710 kOe. The exchange and anisotropy fields may be determined separately because the nuclear anisotropy field, HN, may be calculated and the exchange field obtained from 2H EHN = 2HE× (9.43/T).We are presently investigating the temperature dependence of the resonance field in the helium range. Within the experimental uncertainty of 2%, we...