Microwave Absorption Measurements Research Articles

Magnetization, AC susceptibility and microwave absorption in Dy and TbY alloys

Measurements of magnetization, ac susceptibility and microwave absorption at 9.5 and 35 GHz, have been carried out with single crystals of Dy, Tb 74Y 26, Tb 79Y 21, Tb 81Y 19. These crystals exhibit a stable helix phase at high temperatures; Tb 74Y 26, Tb 79Y 21, also exhibit a low temperature ‘frozen-in’ antiferromagnet state. The critical temperatures T c, T N, and the maximum critical field for the stable helix-ferromagnet transition are, Dy: 80 K, 179 K, 11 kG; Tb 74Y 26: 25 K, 198 K, 9.6 kG; Tb 79Y 21: 93 K, 202 K, 7.4 kG; Tb 81Y 19: 116 K, 205 K, 5.5 kG. Values for the exchange parameter { ▪( Q ) - ▪(0)} estimated from the data are about 0.2 x 10 -3 eV.

Magnetization, AC susceptibility and microwave absorption in Tb and Gd 70Tb 30

Measurements of magnetization, ac susceptibility and microwave absorption at 9.5 and 35 GHz, have been carried out with single crystals of Tb and Gd 70Tb 30. The critical temperatures for Tb were in agreement with previous published results. The Curie Temperature for Gd 70Tb 30 was measured to be (275 ± 2) K. Anisotropy constants have been derived from the microwave measurements. The value of K 2 at 0 K is estimated to 8.8 × 10 8 erg cm -3 (Tb) and 1.3 × 10 8 erg cm -3 (Gd 70Tb 30). At 77 K, the value of K 6 is estimated to be 6 × 10 4 erg cm -3 (Gd 70Tb 30.

Microwave-induced pressure waves in a model of muscle tissue.

Microwave-induced mechanical stress waves were studied in simulated muscle tissue. Pulsed microwave energy at 5.655 GHz induced pressure waves that were recorded with a hydrophone transducer. Each pulse produced a peak power density greater than 1.5 kW/cm2. Microwave absorption measurements within the model showed energy deposition to be mostly confined to a region within 2 cm of the irradiated surface. The average specific absorption rate (SAR) at the surface of the sample was about 100 W/kg. The microwave-induced stress wave propogated at a velocity of 1,600 m/sec with peak pressures of approximately 300 pascals and was detectable after having traveled a total distance of 0.61 m on a path that included two reflections at model-container interfaces.

Microwave Spectroscopy in Semimetallic Bismuth–Antimony Alloys

AbstractResults are given of systematic microwave absorption measurements at 35 and 70 GHz in semimetallic BiSb alloys. The great number of experiments permits to made representative statements on the dependence of the cyclotron masses and the relaxation times of the charge carriers from the Sb concentration. Measurements of the electron‐hole hybrid‐resonance field strengths vs. the antimony concentration (x at% of Sb) show that the band parameters of the holes at T do not substantially vary for x < 6.

Microwave relaxation in polycrystalline garnets at low power levels

Low power microwave absorption and dispersion measurements have been made on a range of polycrystalline YIG samples, pure and rare-earth doped, at 6.0 and 9.2 GHz and at temperatures from room to 150 degrees C. The results are presented in terms of Delta H, the FMR linewidth and Delta Heff, the effective linewidth in applied fields above the spin-wave manifold. Delta Heff was found to be directly proportional to the measuring frequency and to the concentration of the rare-earth ion present. Delta Heff also decreased as the temperature was raised, roughly proportionately with the saturation magnetisation. Measurements on the role of grain size were inconclusive due to the grain size distribution present in the samples. It is suggested that the high-field relaxation behaviour cannot be described by a simple spin-wave model, and a possible explanation is given, based on localised resonances in an independent grain model.

Electrical resistivity and microwave absorption at the spin-reorientation of Fe 3BO 6

Electrical resistivity and microwave absorption measurements near the spontaneous spin-reorientation of Fe 3BO 6 demonstrate that to a good approximation the transition can be considered of being of first order although the width of the transition is different from zero.

The determination of the frequencies of magnetostatic modes in rectangular thin films of ferrimagnetic yttrium iron garnet

The authors have performed calculations of the frequencies of magnetostatic modes in rectangular thin-film specimens of yttrium iron garnet. The calculations have been performed for two sets of film dimensions, one set corresponding to a film on which the authors have done microwave absorption measurements and the other set corresponding to a film on which similar experiments were done previously by Tittmann (1971, 1973). In each case the thickness of the film was 12.0 mu m, and it is possible to obtain an explanation of the experimental results entirely in terms of magnetostatic modes.

Dielectric Relaxation of Some Phenols from Microwave Absorption Measurements

Dielectric Relaxation of Some Phenols from Microwave Absorption Measurements

Frequency dependent microwave absorption in acoustoelectric domains in ZnO

Microwave absorption measurements in theX andR† bands were performed in acoustoelectrically excited ZnO crystals at room temperature. In the resistivity range considered a frequency dependence of this absorption was found, confirming the prediction of the theory, that the microwave absorption in acoustoelectrical domains is mainly determined by the diffusion and the dielectric relaxation times. The experimental results were compared with theory, and average microfields of a strength of 15 kV/cm were obtained. These fields are generally high enough to produce excitonic Franz-Keldysh effect in ZnO.

Dielectric Relaxation of Some Hydroxy-Compounds from Microwave Absorption Measurements

Article Dielectric Relaxation of Some Hydroxy-Compounds from Microwave Absorption Measurements was published on March 1, 1976 in the journal Zeitschrift für Physikalische Chemie (volume 257O, issue 1).

Dielectric Relaxation of Some Hydroxy-Compounds from Microwave Absorption Measurements

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Intramolecular Relaxation Mechanisms of Some Nitro Anilines in Non-Polar Solvents from Microwave Absorption Measurements

Article Intramolecular Relaxation Mechanisms of Some Nitro Anilines in Non-Polar Solvents from Microwave Absorption Measurements was published on April 1, 1975 in the journal Zeitschrift für Physikalische Chemie (volume 95, issue 4-6).

Magnetoresistance and Field-Induced Phase Transitions in the Helical Antiferromagnetic State of Dysprosium

Field-induced magnetic phase transitions in the helical phase of dysprosium have been studied through basal-plane magnetoresistance measurements. Certain details of the measurement technique were found to be of profound importance: it is essential that the sample's internal magnetic field have high homogeneity, and that the single-crystal specimen be mounted in such a way that it may distort freely under the influence of thermal and magnetostrictive stresses. Throughout this investigation, the magnetic field was applied in the basal plane. Anomalies in the magnetoresistance, which are correlated with the field which collapses the helix at a critical value ${H}_{c}$, have been observed. For temperatures greater than 130 \ifmmode^\circ\else\textdegree\fi{}K, and fields greater than ${H}_{c}$, anomalies have been observed which are believed to result from transitions from fan to ferromagnetic ordering. Resistance deviations as large as 4% were observed at 20 kOe, and important to the interpretation of microwave-absorption measurements.

Microwave absorption by bunched carriers in acoustoelectric domains

A theory of the free carrier absorption in acoustoelectric domains is developed by using a generalized current equation and the Poisson equation. The theory is compared with microwave absorption measurements. Using the relative values of the frequency distribution of the acoustic flux in the domains obtained by Brillouin scattering, the absolute values of the AC acoustic potential have been determined from these experiments. The obtained values of the acoustic potential show that gain saturation is not caused by carrier bunching but by parametric conversion processes.

Tunable-Laser Spectroscopy of the ν1 Band of SO2

Individual transitions of the ν1 vibration-rotation band of SO2 in the 8.7-μm-wavelength region have been observed, using tunable semiconductor diode lasers, and compared with theoretical calculations based on pure-rotation data from microwave absorption measurements. A new value of 1151.71 ± 0.01 cm−1 has been found for the ν1-band center. Pressure-broadening coefficients and intensities of individual lines were determined from the high-resolution data, and a value was obtained for total band intensity.

Microwave absorption in a helical polypeptide molecule

Microwave absorption measurements (3, 8.5, 36 and 72 GHz) are reported on three different molecular weight samples of poly(γ-benzyl-L-glutamate), PBLG, in two solvents. In each case a distinct absorption, often quite narrow (the Fuoss-Kirkwood parameter β≃ 1.0), which is almost temperature independent is centred between 2 and 15 GHz. Its frequency, intensity and contour are not inconsistent with a helical-spring mode suggested to account for the abnormal increase in (α‖–α⊥) between the visible and 6 MHz. Other possible origins are considered.

Microwave Magnetoabsorption at Low Temperatures in Semiconducting CdF2

Current models for the observed properties of semiconducting Cd${\mathrm{F}}_{2}$ differ in their predictions of polaron mass ${m}_{p}$. A peak with magnetic field in the low-temperature microwave absorption of semiconducting Cd${\mathrm{F}}_{2}$ has been interpreted in the literature as cyclotron resonance of polarons with ${m}_{p}\ensuremath{\sim}11{m}_{e}$. If such a heavy mass were appropriate, semiconducting Cd${\mathrm{F}}_{2}$ would be unlike any of the conventional semiconductors. The presently reported measurements of microwave absorption as a function of applied magnetic field, impurity concentration, frequency, microwave polarization, and temperature enable us to rule out cyclotron resonance as a possible explanation for the absorption peak. Instead, the effect can be qualitatively interpreted by a model based on covalent bonding between donor impurities.

The Apparent Dipole Moments of Some Symmetrical Molecules from Microwave Absorption Measurements

Article The Apparent Dipole Moments of Some Symmetrical Molecules from Microwave Absorption Measurements was published on April 1, 1971 in the journal Zeitschrift für Physikalische Chemie (volume 246O, issue 1).

Model of the Anisotropic Energy Gap in Superconducting Zinc

Anisotropic energy gap model in superconducting Zn to describe microwave absorption measurements

Complex Susceptibility and Resonance Frequencies of Canted Antiferromagnets

Expressions for the complex susceptibility and resonance frequencies of the two-sublattice model for a canted antiferromagnet are derived. This work is an extension of the analysis given by Herrmann in that (1) the applied field is allowed to have an orientation in the $\mathrm{ac}$ plane, (2) the two sublattice moments are allowed to assume their equilibrium orientations wherever they may be in the $\mathrm{ac}$ plane, (3) phenomenological damping is included, and (4) a magnetocrystalline anisotropy energy term with fourfold symmetry is included. It is found that both the susceptibility and the resonance frequency exhibit an extremely sensitive dependence on the angular orientation of the applied field, when the field is near either the $a$ or the $c$ axis. For precise alignment of the field along an axis, resonance is found for arbitrarily low frequencies. However, the minimum frequency for resonance becomes 10 GHz if the field is 0.03\ifmmode^\circ\else\textdegree\fi{} from the axis for material constants similar to those of TmFe${\mathrm{O}}_{3}$. Simple maxima in both parts of the complex susceptibility occur if the operating frequency is below the minimum resonance frequency in such an off-axis case. With the variety of behavior predicted by this analysis, the microwave absorption measurements in TmFe${\mathrm{O}}_{3}$ by LeCraw et al. can be plausibly interpreted within the framework of the two-sublattice model by postulating inhomogeneities in the orientation of the crystalline axes. The expressions developed in this paper are essential for relating the microwave measurements to material constants as measured by other techniques.