The design of reciprocal ferrite phase shifters

The design of a reciprocal ferrite phase shifter in a rectangular waveguide, using perturbation theory with a quasi-stationary approximation for the field perturbation of the system is considered. The theoretical results are compared with experimental data and with a design carried out without using the quasi-stationary approximation [5], The simplicity of the proposed method and the good agreement between the theoretical and experimental results enable it to be used in solving engineering problems.     

Temperature dependence of the pseudocontact shift in lanthanide shift reagents

The method of calculating the pseudocontact shift of lanthanide shift reagents as a power series of T⁻ⁿ, the reciprocal of temperature, developed by Bleaney has been extended to the T⁻³ term. Using crystal field parameters reported in the literature, it is found that the T⁻³ term is no more than 10% of the T⁻² term in magnitude at room temperature for all ions to which the theory is applicable. The calculations show that even though the pseudocontact shift cannot be fitted exactly to a T⁻² temperature dependence, the simple equation for the T⁻² term is adequate for estimating the actual shift at room temperature to an accuracy of 10 to 20%.     

Temperature dependence of anisotropy in monocrystalline lithium ferrite films

A study of crystallographic and uniaxial anisotropy in monocrystalline Li-ferrite films in the temperature range 4.2–550°K is presented. The experimental results K₁(T) agree well with calculations based on the one ion model with crystalline field coefficients of a_A=–2.77 ·10^–2 cm^–1, a_B=3.34 · 10^–2 cm^–1. An experimental function K_u(T) is obtained which does not contradict the assumption that anisotropic stresses are responsible for the development of uniaxial anisotropy in Li-ferrite films.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 113–116, August, 1973.     

Temperature dependence of magnetic anisotropy constant in cobalt ferrite nanoparticles

The temperature dependence of the effective magnetic anisotropy constant K(T) of CoFe₂O₄ nanoparticles is obtained based on the SQUID magnetometry measurements and Mössbauer spectroscopy. The variation of the blocking temperature T_B as a function of particle radius r is first determined by associating the particle size distribution and the anisotropy energy barrier distribution deduced from the hysteresis curve and the magnetization decay curve, respectively. Finally, the magnetic anisotropy constant at each temperature is calculated from the relation between r and T_B. The resultant effective magnetic anisotropy constant K(T) decreases markedly with increasing temperature from 1.1×10⁷ J/m³ at 5 K to 0.6×10⁵ J/m³ at 280 K. The attempt time τ₀ is also determined to be 6.1×10⁻¹² s which together with the K(T) best explains the temperature dependence of superparamagnetic fraction in Mössbauer spectra.     

Temperature dependence of the positive-muon knight shift in MnSi

The temperature dependence of the μ⁺ Knight shift in weakly-helimagnetic MnSi has been measured in the temperature range between 28 and 300 K. The observed shift is found to be directly proportional to the host susceptibility in the paramagnetic state with a hyperfine coupling constant of —4.8 kOe/_μB.     

Temperature dependence of Raman linewidth and shift in CuI

The temperature dependence of the optical phonon linewidth and frequency shift in CuI has been measured in the temperature range of 4.2 ～ 300 K. Utilizing phonon dispersion curves obtained from neutron scattering measurements, the linewidths and frequency shifts are calculated in terms of three-phonon interactions proposed by Pine and Tannenwald. The experimental results for the change in linewidth and frequency with temperature are in good agreement with this theory.     

Temperature dependence of the isomer shift in white tin

The OPW method is used to study the temperature-dependent isomer shift of β-Sn above the room temperature from the contributions including both the crystal pseudopotential with the Debye-Waller factor and the self-energy effect. It is shown that, although the self-energy contribution to the absolute value of the isomer shift in β-Sn is negligibly small, its rate of change with respect to temperature is at least of the same order, but with different sign, as that of the Debye-Waller factor term. We conclude that the increase in the isomer shift of β-Sn with temperature observed experimentally can be well accounted for by the effect of self-energy interactions.     

Temperature dependence of diffuse field phase

Diffuse fields, which have scattered from microstructure or reflected from walls so much as to prohibit conventional analyses, are usually examined by means of the time evolution of their ultrasonic spectral energy density. The phase information is usually discarded as resisting analysis. The phase, while unpredictable is, however, robust; according to theory it remains constant if source and receiver are not disturbed. Nevertheless, in practice we do observe slow drifts of phase over time scales of minutes. Here we examine the hypothesis that the phase drifts are due to temperature fluctuations. Temperature changes on cooling from 40 degrees C to room temperature were monitored and compared with changes in diffuse field phase. It was found that the reverberant ultrasonic field in a 7 cm aluminum block evolves with temperature in a manner that is in accord with published data on the temperature dependence of the ultrasonic velocities. Our 1 MHz transient source gives rise to a complex waveform that is observed to undergo an almost pure dilation. The precision with which this shift can be measured approaches 20 ns. This is remarkable when compared with the 100 ms travel time of the signal. Thus the temperature dependence of elastic wave speed is measured with a precision limited by the precision of one's thermometer. The signal is also found to suffer some distortion which, it is suggested, is related to the different rates of change of longitudinal and shear speeds. The corresponding prediction for the degree of distortion is found to be in accord with measurements.     

Frequency dependence of the phase shift in optical-fibre thermal modulators

The optical phase shift as a function of frequency was determined in the range from DC to >10 kHz for some single-mode optical-fibre phase modulators, formed by depositing a metal layer on the cladding surface by vacuum evaporation. A thermal analysis is presented in which the fibre surface and core temperatures are determined as a function of the frequency of the heating due to an electric current passing through the coating. The phase modulation arises from a combination of the temperature change at the core (predominant at low frequencies) and strains produced by the thermal expansion of the metal coating (predominant at the high frequencies). Applications include phase and birefringence control in optical-fibre interferometers.     

Temperature dependence of the Knight shift for cadmium in palladium

The Knight shift and its temperature dependence for a Cd impurity in palladium metal were measured by means of DPAD- and DPAC-methods utilizing the well known 5/2⁺, 247-keV state in¹¹¹Cd. The shift at 80 K was found to be KS (CdPd, 80 K)=?0.8(2)%. The observed variation of the KS in the temperature range from 80 K up to 1400 K is 0.5%. For calibration purposes an accurate remeasurement of the magnetic moment of the 5/2⁺ state in¹¹¹Cd was necessary and yieldedμ(¹¹¹Cd, 5/2⁺, 247 keV)=?0.7697(20) n.m.     

Temperature dependence of the Mössbauer isomer shift

The isomer shift for nuclei in solids is calculated taking into account the core electron charge density, the overlap effects, the charge transfer effects, and the crystal field effects. The importance of the dynamical electron phonon interaction is pointed out. It is found that the phonon-induced dynamical configurational mixing and the dynamical charge transfer play an important role and contribute to a dynamical isomer shift which enhances the temperature-dependent second-order Doppler shift. It is found that the internal conversion and the electron capture give information which is related to the isomer shift. In mixedvalence compounds such as EuCu₂Si₂, the center shift of the M?ssbauer lines has been explained as if arising from the phonon-induced dynamical isomer shift.     

Polarization conversion in ring resonator phase shifters

The effect of the polarization rotation induced by curved waveguides on the spectral behavior of phase shifter ring resonators is investigated both theoretically and experimentally. At resonance the polarization rotation that takes place in curved waveguides is strongly enhanced. The effect can be detrimental, or it can be exploited for new devices. The ring vectorial transfer function is derived, together with the conditions for the total conversion of TE polarization into TM polarization. These conditions are verified experimentally.     

Temperature dependence of coherent oscillations in Josephson phase qubits

We experimentally investigate the temperature dependence of Rabi oscillations and Ramsey fringes in superconducting phase qubits. In a wide range of temperatures, we find that both the decay time and the amplitude of these coherent oscillations remain nearly unaffected by thermal fluctuations. In the two-level limit, coherent qubit response rapidly vanishes as soon as the energy of thermal fluctuations k(B)T becomes larger than the energy level spacing variant Planck's over h omega of the qubit. In contrast, a sample of much shorter coherence times displayed semiclassical oscillations very similar to Rabi oscillation, but showing a qualitatively different temperature dependence. Our observations shed new light on the origin of decoherence in superconducting qubits. The experimental data suggest that, without degrading already achieved coherence times, phase qubits can be operated at temperatures much higher than those reported till now.     

Temperature and field dependence of the order parameter in the antiferroquadrupolar phase of CeB6 from mu+ Knight shift measurements

The Fermi contact hyperfine contribution to the Knight shift of positive muons, implanted at the interstitial 3d sites in CeB6, is found to exhibit the same temperature dependence below T(Q) in phase II as the quadrupolar order parameter determined from resonant and nonresonant x-ray scattering. Furthermore, the contact coupling parameter is shown to be anisotropic and field dependent. These unanticipated features are interpreted to arise from the RKKY induced conduction electron spin polarization, which depends on the orientation and expectation value of the ordered 4f quadrupole moments.     

Temperature dependence of the knight shift of Ag in Pd measured by DPAD-techniques

The temperature dependence of the Knight shift of Ag in palladium has been observed between 80 K and 1000 K and is proportional to that of the susceptibility of Pd. The shift at 80 K is K = -1.4(3)%. The measurements were performed by observing the perturbed angular distribution of γ-rays following a nuclear reaction (DPAD).     

Temperature dependence of magnetization of pyrrhotines in a metastable phase state

Magnetic properties of iron sulfides in a metastable phase state were investigated. During heating of iron sulfides of the composition Fe_0.901S up to 150°C a magnetization increase was observed. It was shown that the observed effect is not the known transition and that it results from the redistribution of vacancies of iron ions in basal planes of the crystal structure of the NiAs type. A theoretical model was proposed which explains qualitatively this effect.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 56–61, April, 1989.     

Study of contributions to temperature dependence of the phase shift in an electro-optic crystal

The spontaneous and electric field induced phase retardations have been measured as a function of temperature in a KDP crystal using an accurate method. The plots of these retardations versus temperature reveal unexpected undulations. We consider the various contributions which could be involved in these dependences, such as the thermo-optic effect, crystal dilatation and temperature dependence of the electro-optic coefficient. By means of calculations, the undulations are shown to be caused by an interference phenomenon related to light reflections on the surface of the crystal. This revised version was published online in November 2006 with corrections to the Cover Date.