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1.
We report on the magnetic-field-dependent optically detected magnetic resonance (ODMR) spectra for polycrystalline samples
of the bridged Zr(IV) metallocenes, Me2Si<(Cp2)ZrCl2 ( (dimethylsilylbis(cyclopentadienyl)zirconium-dichloride) and Me2C<(Cp2)ZrCl2 (iso-propylidenebis(cyclopentadienyl)zirconium-dichloride). ODMR spectra at zero magnetic field were recorded by frequency
sweeping a microwave source from 0.1 to 10 GHz with the sample contained in a microwave helix. ODMR spectra at finite magnetic
fields were recorded with the sample contained in either a helix or a slotted-tube resonator with a fixed microwave frequency
and sweeping the magnetic field. For all experiments, the sample and microwave probes were contained in an immersion dewar
cryostat, and the temperature was held at about 2 K. All three zero field ODMR transitions (2|E|, and |D| − |E| and |D|+|E|) were observed in the frequency-swept ODMR spectra recorded at zero and small magnetic fields. The zero-field frequency-swept
spectra allowed the determination ofD andE values uniquely. For frequency-swept small-field ODMR spectra recorded at successively higher magnetic fields, each of the
ODMR line intensities was observed to increase with increasing magnetic field. This intensity increase was observed for all
three ODMR lines, reflecting an increase in the total intensity rather than simply a change in the polarization of the triplet
sublevels. The latter would result in a change in the relative intensities of the ODMR lines but would not change simultaneously
the intensities of all three lines. The ODMR line intensities increase in proportion toB
n, wheren<1. This field dependence is weaker than the expected proportionalB
2 dependence from the Zeeman effect, which likely originates from the magnetic field dependence of the spin relaxation rates
between the triplet sublevels. Magnetic-field-swept ODMR spectra recorded at fixed microwave frequencies in the X-band frequency
range (9.8 GHz) do not show all three expected classic Pake powder pattern line shape profiles, exhibited by the molecules
with their magneticZ, Y, andX axes parallel to the external magnetic field. In particular, the intensity for molecular magneticY-axes parallel to the external magnetic field is completely suppressed. In addition, an external magnetic field dependence
in field-swept ODMR spectra was observed, which results in a linear decrease of the ODMR intensity with increasing strength
of the external magnetic field over and above that would be expected in a polycrystalline spectrum. The data are analyzed
by simulation of the continuous-wave ESR spectrum with the eigenvalues and eigenvectors of the spin Hamiltonian matrix characterizing
the triplet state exhibiting the ODMR spectrum, in conjunction with homotopy, as a function of the orientations of the magnetic
axes of the various molecules in a polycrystalline sample. This approach is useful to interpret the experimentally observed
ODMR transition frequencies andg-values but does not take the amplitudes in the ODMR spectrum. The corrections required to modify the continuous-wave ESR
spectral amplitudes that reproduce the observed ODMR amplitudes are effects associated with the ODMR processes. 相似文献
2.
V. N. Zirakashvili 《Journal of Experimental and Theoretical Physics》1998,87(2):218-222
A variational method is used to obtain estimates of the effective particle transport coefficients in a random static magnetic
field. The particle propagation is described by an anisotropic diffusion equation. The diffusion coefficient parallel to the
local magnetic field is much greater than the transverse diffusion coefficient. For large-scale magnetic-field variations
the diffusion is described by effective coefficients. The variational approach can be used to find the effective parallel
and perpendicular diffusion coefficients. It was shown that the instability growth rate of the magnetic field lines determines
the upper estimate of the effective transverse diffusion coefficient.
Zh. éksp. Teor. Fiz. 114, 398–405 (August 1998) 相似文献
3.
We present here an order of magnitude calculation for the coefficients of viscosity with the assumption that the drift velocity
introduces asymmetry both in the single-particle distribution functionf
1 and the correlation functionP(1, 2). These asymmetric parts have been estimated considering the self-relaxation of the system when the cause of drift velocity
is suddenly removed. Using these, the kinetic part of the coefficient of electron viscosity has been calculated and the result
fairly agrees with similar studies by others. The potential part of shear viscosity coefficient is found to be zero while
both parts of the coefficient of bulk viscosity are non-zero. 相似文献
4.
设计了外Q值较小,工作于高阶横磁TM310模的X波段速调管单间隙同轴输出谐振腔。用微波等效电路理论计算了高阶横磁TM310模情形六个漂移管的等效间隙中心位置,由此计算腔内等效间隙中心到输出波导内横向膜片的等效长度。以MATLAB编程计算得到同轴谐振腔TM310模式加载矩形波导滤波器输出回路的间隙阻抗,其结果与传统冷测模拟法计算结果吻合。验证了等效长度计算方法的正确性,用于圆柱腔基模的传统微波等效电路理论能用于分析同轴谐振腔高阶横磁模式输出回路,且比传统的冷测模拟法及场分析法更为快捷。 相似文献
5.
Yuting Liu Jie Jiao Lingying Li Jiashuai Ma Bo Ren Jianwei Chen Wenning Di Xiangyong Zhao Haosu Luo Ling Shi 《固体物理学:研究快报》2014,8(2):194-197
The nonlinear and linear properties in Metglas/piezofiber magnetoelectric composites under DC bias fields (Hbias) have been investigated via a frequency‐conversion technique. It was found that the major noise near the carrier frequency (fC) is caused by the driven source. Both linear ME coefficient and noise floor near fC (bandwidth of noise measurement is 10 Hz) were dependent on Hbias, while the nonlinear ME coefficient was independent. A high magnetic‐field sensitivity of 40 pT was obtained after optimizing Hbias. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
6.
S. K. Misra 《Applied magnetic resonance》2005,28(1-2):55-67
A matrix technique to calculate signals recorded using the microwave amplitude-modulation technique is described. The calculations are carried out for spin packets, on and off resonance, to take into account inhomogeneous broadening. Both, the transverse component of magnetization representing the continuous-wave signal in a resonator, such as a cross-looped resonator, as well as the signal (electromotive force) induced in a pickup coil oriented parallel to the external magnetic field, are calculated for an arbitrary value of the coefficient of modulation. This is accomplished by solving the relevant Bloch equations in the rotating frame for the case when the amplitude of the microwave field is modulated by a sinusoidal wave, using Fourier expansions of the longitudinal and transverse components of the magnetization in Bloch equations. This results in a series of coupled equations inM α(n) (α=y,zz), the magnetic moments of vaarious orders, leading to a penta-diagonal matrix of infinite dimension. These equations are then truncated and solved by a fast matrix technique to calculateM α(n), required to calculate the modulation signals as functions of the amplitudemodulation frequency Ω. It is outlined how to exploit the expressions for the modulation signals to estimate the spin-lattice relaxation timesT 1 and spin-spin relaxation timesT 2 accurately by the leastsquares procedure, fitting simultaneously all signals obtained for spin packets, on and off resonance, at various modulation frequencies. Illustrative examples are provided. 相似文献
7.
Thermal noise in Hg0.795Cd0.205Te detectors is estimated for large biasing fields at a lattice temperature of 77 K, by computing the correlation functions of the velocity fluctuations with the Monte Carlo technique. The noise temperature for current components transverse to the field is almost independent of the field, but that corresponding to the parallel component increases by a factor of about 1.3 at 50 V/cm and by a factor of 3.0 at 300V/cm. The thermal noise voltage for a detector of 85 resistance increases from 0.6nV/Hz1/2 at low biasing fields to about 3nV/Hz1/2 at a field of 300 V/cm. The noise power is also found to remain constant up to about 75 GHz, and it decreases thereafter by a factor of 0.25 for doubling of the frequency. 相似文献
8.
L. Krlín 《Czechoslovak Journal of Physics》1969,19(9):1076-1091
The form of the distribution functionf (P
i, Qi,t) is determined in terms of the integralW of the diffusion equation and of the initial distribution functionf
0(P
i, Qi, t).W gives the probability of the occurrence of a particle in the phase space Pi, Qk.The Hamiltonian function of the particle and the distribution functionf obtained in the above way are used for establishing the value of the absorbed energy and the rate of absorption in the case of the homogeneous magnetostatic fields. We discuss the conservative r.f. field-particle system (also in the nonlinear approximation), the effect of the nonlinearity of the diffusion tensor and the meaning of the resonance for the rate of absorption. We discuss also shortly the effect of the external stochastic field on the stability of plasma, already mentioned in earlier literary sources.The author wishes to thank Dr. J. Lacina for valuable discussions. 相似文献
9.
Effects of signal modulation and coloured cross-correlation of coloured noises on the diffusion of a harmonic oscillator
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The diffusion in a harmonic oscillator driven by coloured noises
$\xi(t)$ and $\eta(t)$ with coloured cross-correlation in which
one of the noises is modulated by a biased periodic signal is
investigated. The exact expression of diffusion coefficient d as a
function of noise parameter, signal parameter, and oscillator
frequency is derived. The findings in this paper are as follows. 1)
The curves of d versus noise intensity D and d versus noises
cross-correlation time $\tau_3$ exist as two different phases. The
transition between the two phases arises from the change of the
cross-correlation coefficient $\lambda$ of the two
Ornstein--Uhlenbeck (O-U) noises. 2) Changing the value of $\tau_3$, the curves of d versus Q, the intensity of colored noise
that is modulated by the signal, can transform from a phase having a
minimum to a monotonic phase. 3) Changing the value of signal
amplitude A, d versus Q curves can transform from a phase
having a minimum to a monotonic phase. The above-mentioned results
demonstrate that a like noise-induced transition appears in the
model. 相似文献
10.
The temperature dependence of the thermal expansion for GaAs and InP is investigated theoretically using the experimental pressure derivatives of elastic stiffness constants and phonon frequencies. The linear correlation between the transverse acoustical mode Grüneisen parameter γXTA and the metallic transion pressure Pt obtained by Weinstein is not satisfied for GaAs and InP, but the observed thermal expansion of GaAs is well reproduced. In addition, the linear expansion coefficient of InP is predicted theoretically as a function of temperature. Then, the phonon dispersion curves of GaAs and InP at their covalent-metallic transition pressures are quantitatively shown. 相似文献
11.
R. F. Kiefl J. Sonier D. A. Bonn J. H. Brewer J. F. Carolan K. H. Chow P. Dosanjh W. N. Hardy Ruixing Liang W. A. MacFarlane P. Mendels G. D. Morris T. M. Riseman J. W. Schneider 《Hyperfine Interactions》1994,86(1):537-542
We report precision transverse fieldSR measurements of the internal field distribution in the vortex state of crystalline YBa2Cu3O6.95. A novel low background apparatus was used to study a mosaic sample of three high quality single crystals (Tc=93.3K). The observed frequency spectra in magnetic fields of 5kG and 15 kG applied along the c-axis have the characteristic features expected for a regular vortex lattice with some additional broadening. From a preliminary analysis we find that [(0)/(T)]2 has a linear temperature coefficient forT<30 K. Such a term is inconsistent with simple s-wave pairing in the superconducting state. These results support recent microwave measurements of(T) on similar crystals in zero applied field but differ significantly from previousSR reports on sintered powders and crystals with lower Tc.This research was supported by the Natural Sciences and Engineering Research Council of Canada. 相似文献
12.
K. Aggarwal L. Asch F. N. Gygax O. Hartmann G. M. Kalvius A. Kratzer F. J. Litterst K. Mattenberger A. Schenck O. Vogt 《Hyperfine Interactions》1989,51(1-4):933-942
The materials crystallize in the NaCl structure. UP undergoes at 122 K a first order transition into a type I single-k antiferromagnetic
state, followed by a second first order transition into a type I double-k-structure at 22 K. UTe is a ferromagnet withT
c
=104 K. The two first order transitions of UP reveal themselves by abrupt changes of the transverse field damping rate. No
spin rotation is observed in zero field for both antiferromagnetic spin structures which is in keeping with point dipolar
lattice sums. In UTe we observe the characteristic critical behavior: a rapid increase of damping rate and paramagnetic frequency
shift when approachingT
c
from above. In the ferromagnetic regime the spin rotation in zero field damps out too rapidly to be observed.
This work has been funded in part by the German Federal Minister for Research and Technology (BMFT) under contract Nr. 03-KA1-TUM-4. 相似文献
13.
Current-voltage characteristics of a system with a variable number of slipping phase centers resulting from phase separation
in a tin whisker under external microwave field with a frequency Ω/2π≅35–45 GHz have been studied experimentally. Emergence and disappearance of steps with zero slope in a whisker’s current-voltage
characteristic at U
m/n
=(m/n)U
Ω, where m and n are integers and U
Ω is determined by Josephson’s formula ℏΩ=2eU
Ω, have been investigated. Microwave field generated by slipping phase centers is nonharmonic, and the system of slipping phase
centers permits synchronization of internal oscillations at a microwave frequency by an external field with a frequency which
is the n-th harmonic of internal oscillations. The estimated microwave power generated by a whisker is 10−8 W. Stimulation of superconductivity in a current-carrying whisker has been detected.
Zh. éksp. Teor. Fiz. 113, 1364–1375 (April 1998) 相似文献
14.
The current voltage characteristics and the dependence of the transverse electric field on applied voltage is studied experimentally and theoretically forn-Si at 27 K for the current close to the <111>-direction. A solution in form of a loop is split off from the solution with nearly equal carrier population in all three valleys and corresponds to predominant population of only one valley. The solutions corresponding to predominant population of either one of the three valleys may coexist in the sample in the form of layers parallel to the current. A transverse magnetic inductionB may change the size of the layers and by appropriateB it is possible to induce either one of these three layers or any combination of them into the sample. 相似文献
15.
In many-valley semiconductors for certain specific orientations of the applied electric field E, the different drift velocities of electrons in different valleys should give rise to an additional diffusion called intervalley diffusion. Experimental evidence of this effect is presented. This was obtained by measuring the longitudinal diffusion coefficient of electrons in Ge, at 77 and 190 K, for E parallel to the 〈100〉 and 〈111〉 directions. The interpretation of the effect has been confirmed by Monte Carlo calculations. 相似文献
16.
G. G. Fedoruk 《Journal of Experimental and Theoretical Physics》2005,100(6):1069-1074
Two-photon transient nutation is observed in a two-level spin system (E′1 centers in crystalline quartz) using a transverse microwave field and a linearly polarized rf field oriented along a static magnetic field in the electron paramagnetic resonance. Nutation is excited when the sum of the energies of a microwave photon and a rf photon is equal to the energy difference between two spin states. The two-photon nature of nutation is confirmed by measuring its frequency as a function of the amplitude and frequency of the rf field as well as the amplitude of the microwave field. The amplitude of the effective field of two-photon transitions is measured. It is shown that the decay rate of two-photon nutation is close to the decay rate for one-photon nutation and is determined by the spin-spin interaction between E′1 centers. 相似文献
17.
The microwave electromagnetic properties of Co2-Y hexagonal ferrite single rod and paired rods are demonstrated using a standard waveguide method. With the sweeping of the bias magnetic field, the ferromagnetic resonance occurs twice in the transmission spectra of single ferrite rod, which are induced by the self-bias magnetization and the external field magnetization, respectively. The zero/low-field resonance is determined by the shape anisotropy mainly, and disappears as the rod?s aspect ratio is relatively low. For the paired rods, when the interval between two parallel rods is small, the zero/low-field resonance vanishes due to the dipolar interaction between two rods. 相似文献
18.
M. Deb Roy B. R. Nag D. Chattopadhyay 《Applied Physics A: Materials Science & Processing》1983,32(1):39-43
Monte-Carlo results on the velocity-field characteristics, ac diffusion-constant and thermal-noise voltages are presented for In0.765Ga0.235As0.5P0.5 at 300K. Recently available values of physical constants have been used in the calculations. The values of diffusion constants are close to those of InP but the thermal noise voltages are found to increase faster with the field. The peak velocity is 1.9 × 107 cm/s and the threshold field for negative differential mobility is about 6 kV/cm. 相似文献
19.
M. Rimini-Döring A. Hangleiter S. Winkler N. Klötzer 《Applied Physics A: Materials Science & Processing》1992,54(2):120-123
We report on temperature (77 to 300 K) and voltage dependent low frequency (100 Hz to 100 kHz) noise behavior of InGaAs/InP photodiodes in non-equilibrium steady state. In addition to common white, 1/f, and Lorentz noise we are able to observe for the first time minima and maxima in the photocurrent noise spectra. The recombination of a pair of free carriers through a recombination center at the heterointerface provides the correlation between the electron and hole ensembles necessary to explain the observed noise reduction. 相似文献
20.
Kh. K. Aliev I. K. Kamilov Kh. I. Magomedgadzhiev M. -G. K. Omarov 《Physics of the Solid State》1997,39(2):296-297
The absorption coefficient α
k for longitudinal ultrasonic (15 MHz) waves propagating transverse to the direction of a magnetic field H is measured in single crystal gadolinium. It is found that in fields H⩽600 Oe, the peak in α
k is shifted toward lower temperatures, while the absolute magnitude of the absorption rises with increasing H. It is shown on the basis of dynamic scaling that the anomalous behavior of α
k in fields H⩽600 Oe can be explained by introducing a magnetic field analog of the Landau-Khalatnikov relaxation mechanism.
Fiz. Tverd. Tela (St. Petersburg) 39, 339–340 (February 1997) 相似文献