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1.
The influence of interaction between anisotropic γ-Fe2O3 nanoparticles on their coercive force H
c
is studied. In samples where the degree of homogenization of anisotropic γ-Fe2O3 nanoparticles is high owing to mechanical, ultrasonic, and magnetic dispersion with subsequent filtering of resulting suspensions,
H
c
is almost independent of volume concentration η of the particles when η varies between 4 × 10−4 and 10−1. In samples homogenized only mechanically, the H
c
versus logη dependence is linear. 相似文献
2.
B. S. Dumesh M. I. Kurkin S. V. Petrov A. M. Tikhonov 《Journal of Experimental and Theoretical Physics》1999,88(6):1221-1228
The spectrum and intensities of NMR lines are investigated experimentally and theoretically for excitation by an alternating
magnetic field h‖ parallel to a static field H in the quasi-one-dimensional, six-sublattice antiferromagnet CsMnBr3. According to theory, two new NMR lines, which are not excited by a transverse magnetic field h
⊥, are observed near the phase transition from triangular to collinear structure (H=H
c
) [JETP 86, 197 (1998)].
Zh. éksp. Teor. Fiz. 115, 2228–2241 (June 1999) 相似文献
3.
Z. V. Golubenko L. P. Ol’khovik Z. I. Sizova A. S. Kamzin 《Physics of the Solid State》1998,40(7):1178-1181
An investigation was made of the magnetic state of a system of highly anisotropic BaO · 6Fe2O3 nanocrystals several lattice parameters thick and having a near-critical volume (∼10−18 cm3), obtained using cryochemical technology. It is observed that the particles are transformed to the superparamagnetic state
and it is shown that the external magnetic field plays a role in its formation. An H-T diagram was obtained for the temperature range 300 K-T
c, which shows various regions uncharacteristic of the macro-object, which are specifically attributed to the distribution
over the anisotropy fields in the system and the impaired magnetic structure in the surface zone of the particles. Relatively
large regions of magnetic fields and temperatures were observed where reversible rotation of the magnetization vector of particles
with near-critical volume plays an important role.
Fiz. Tverd. Tela (St. Petersburg) 40, 1294–1297 (July 1998) 相似文献
4.
Conical refraction, which is due to the renormalization of the elastic moduli by the effective magnetoelastic interaction
and depends on the static magnetic field, has been experimentally observed in an α-Fe2O3 trigonal easy-plane antiferromagnet in addition to the usual internal conical refraction of transverse elastic waves propagating
along the trigonal C
3 axis. It has been shown that the deviation angle θη of the energy flux from the C
3 axis at the internal conical refraction is independent of the magnetic field applied in the basal plane (H ⊥ C
3) and is a constant determined by the ratio of the elastic moduli C
14 and C
44. The deviation angle of the energy flux at the antiferromagnetic conical refraction increases with the magnetic field and
approaches the value θη at large H values. The results are well described by the theory of this phenomenon developed by E.A. Turov and confirm its basic conclusions. 相似文献
5.
Yu. N. Ovchinnikov A. M. Dyugaev 《Journal of Experimental and Theoretical Physics》1999,88(4):696-709
The magnetic field dependence of the average spin of a localized electron coupled to conduction electrons with an antiferromangetic
exchange interaction is found for the ground state. In the magnetic field range μH∼0.5T
c
(T
c
is the Kondo temperature) there is an inflection point, and in the strong magnetic field range μH≫T
c
, the correction to the average spin is proportional to (T
c
/μ H)2. In zero magnetic field, the interaction with conduction electrons also leads to the splitting of doubly degenerate spin
impurity states.
Zh. éksp. Teor. Fiz. 115, 1263–1284 (April 1999)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor 相似文献
6.
A. V. Lazuta 《JETP Letters》1997,65(4):363-368
Recent results on the effect of magnetic field on the sound velocity V in aluminosilicate glasses doped with dysprosium are analyzed on the basis of a minimal model for the ground state of Dy3+ (Kramers ion with J=15/2) described by a wave function ϕ
± = ϕ
±
J
m + ηϕ
± 1/2. The first term represents a state with a large J projection on the local crystal field axis and the random parameter η(〈η〉=0, 〈η
2〉≪1) introduces a small admixture of the state ϕ
±1/2 into the ground state. The relative variation of V due to the resonance interaction of sound waves with this state split by H is determined as a function of H and T. It possesses a universal asymptotic behavior. Our results are in reasonable agreement with the experiment. A possible structure
of the crystal fields that can induce this state is discussed.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 4, 341–346 (25 February 1997)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
7.
8.
V. I. Al’shits E. V. Darinskaya O. L. Kazakova E. Yu. Mikhina E. A. Petrzhik 《JETP Letters》1996,63(8):668-673
A magnetic induction threshold B
c above which the magnetoplastic effect — depinning of dislocations from paramagnetic pinning centers — can be observed in
samples placed in a magnetic field is predicted and observed in Al, NaCl, and LiF crystals. The existence of a threshold is
associated with the fact that for B<B
c the spin-lattice relaxation time τsl in a dislocation-paramagnetic-center system is less than the time required for spin evolution in a magnetic field resulting
in the removal of the spin forbiddenness of an electronic transition that “switches off” the dislocation-pinning-center interaction.
It is shown that the threshold field B
c is sensitive to temperature and x-ray irradiation of the samples. A new method for measuring the spin-lattice relaxation
time in paramagnetic centers on dislocations is proposed on the basis of the data obtained.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 8, 628–633 (25 April 1996) 相似文献
9.
The critical current J
c(θ) of an intergrain boundary is calculated as a function of the contact misorientation angle θ of the granules. It is assumed that the ordering parameter is suppressed in regions near boundaries with an enhanced mechanical
stress induced by randomly distributed surface dislocations. The stress distribution function is determined using a probabilistic
approach. Assuming that the weak coupling at the boundary is Josephson coupling, an analytic expression is found for the angular
dependence J
c(θ) (for tilt and twist boundaries). The magnitude of the residual critical current of a boundary in a strong magnetic field
is estimated.
Fiz. Tverd. Tela (St. Petersburg) 40, 393–402 (March 1998) 相似文献
10.
A. M. Satanin S. V. Khor’kov V. V. Skuzovatkin 《Journal of Experimental and Theoretical Physics》1997,85(2):351-359
We study the effect of a weak nonlinearity in media on the linear regime of current flow in two-dimensional periodic structures
with two equal component concentrations. We find that the asymptotic behavior of the electric field and current as functions
of the distance between the angles in heterogeneous media is determined by the parameter h=σ
2/σ
1 (here σ
1 and σ
2 are the linear conductivities of the cells) and the external magnetic field B. This dependence leads to divergence of the higher-order moments of field and current at certain critical values h
c and B
c and to divergence of the response functions related to the higher-order moments. For square cells the effective nonlinear
conductivity diverges at h⩽h
c, with
. For structures of general shape we find the dependence of h
c on the angles and the external magnetic field. We show that for a given structure the linear regime of current flow in the
system can be reversibly transformed into a nonlinear one by varying the magnetic field strength. The critical field B
c is approximately determined from the condition ω
c
τ∼1, where ω
c and τ
−1 are, respectively, the cyclotron frequency and the collision rate. Finally, we discuss the feasibility of detecting these
effects experimentally.
Zh. éksp. Teor. Fiz. 112, 643–660 (August 1997) 相似文献
11.
Krzysztof Rȩbilas 《Foundations of Physics Letters》2006,19(4):337-351
The Coulomb force, established in the rest frame of a source-charge Q, when transformed to a new frame moving with a velocity V has a form F = q
E + q
v × B, where E = E′∥ + γE′⊥ and B = (1/c
2)v × E and E′ is the electric field in the rest frame of the source. The quantities E and B are then manifestly interdependent. We prove that they are determined by Maxwell's equations, so they represent the electric
and magnetic fields in the new frame and the force F is the well known from experiments Lorentz force. In this way Maxwell's equations may be discovered theoretically for this
particular situation of uniformly moving sources. The general solutions of the discovered Maxwell's equations lead us to fields
produced by accelerating sources. 相似文献
12.
R. L. Lichti T. R. Adams D. W. Cooke R. S. Kwok C. Boekema J. C. Lam D. E. Farrell N. Bansal 《Hyperfine Interactions》1991,63(1-4):73-79
Muon spin relaxation (μSR) data taken at LAMPF on ac-axis oriented fine powder sample of YBa2Cu3O7−δ (YBCO) embedded in epoxy are analyzed for relaxation rate anisotropy. Clear differences beyond simple magnetic field penetration
depth anisotropy are observed forB‖c andB
c. The low-temperature anisotropy ratio is consistent with oriented ceramic data. Small crystallite size and anisotropic flux
pinning characteristics are suggested as the fundamental cause of the additional effects. 相似文献
13.
A theoretical framework for treating the effects of magnetic fieldH on the pairing theory of superconductivity is considered, where the field is taken in an arbitrary direction with respect
to crystal axes. This is applicable to closed, as well as open normal state Fermi surface (FS), including simple layered metals.
The orbital effects of the magnetic field are treated semiclassically while retaining the full anisotropic paramagnetic contribution.
Explicit calculations are presented in the limits |H| → |H
c2(T)|,T ∼ 0 andT →T
c(|H|), |H| ∼ 0. Effects of weak nonmagnetic impurity scattering, without vertex corrections, have also been taken into account in a
phenomenological way. The final results for the case of open FS and layered materials are found to differ considerably from
those of the closed FS. For example, an important parameter,h(T=0)=|Hc2(0)|/[-Tδ|H
c2
T|δT]T{s0} for the case of a FS open ink
z-direction with thek
z-bandwidth, 4t
3, very small compared to the Fermi energy,E
F, is close to 0.5906, compared to 0.7273 for the closed FS, in the clean limit. Analytical results are given for the magnetic
field dependence ofT
c and the temperature dependence of H
c2 for a model of layered superconductors with widely open FS. For a set of band structure parameters for YBa2Cu3O7 used elsewhere, we find reasonable values for the upper critical fieldH
c2(0), the slope (dH
c2/dT)T
c0, anisotropic coherence lengths ζi(T=0),i=x, y, z, and (dT
c/d|H|)|H| → 0. 相似文献
14.
It is found that the bulk part ω of the magnetostriction near the Curie temperature T
c
in a La0.7Sr0.3MnO3 single crystal with the perovskite structure is negative and that the temperature dependence of |ω| has a maximum near T
c
. The quantity |ω| at the maximum increases rapidly with increasing magnetic field. The thermal expansion coefficient near
T
c increases with temperature much faster than linearly. The paramagnetic Curie temperature determined from the Curie-Weiss
law, which the paramagnetic susceptibility of this crystal satifies, was found to be lower than T
c
. These anomalies and also the near-T
c
metal-insulator transition which is characteristic for this material are explained by the existence of a magnetically two-phase
state consisting of a conducting ferromagnetic matrix containing antiferromagnetic insulating microregions occupying not more
than 5% of the sample volume.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 6, 449–453 (25 March 1997) 相似文献
15.
The NMR of 55Mn in the quasi-one-dimensional noncollinear anti-ferromagnet CsMnI3 is investigated at T=1.3 K in magnetic fields up to ∼80 kOe and angles between the field and C
6 axis ϕ≈ 0.5° and ϕ=7°. A new reorientational magnetic phase transition is observed in a field H
c1≈39.0 kOe. The magnetic structure for H>H
c1 is determined. The average Mn2+ spins of the magnetic sublattices in the new phase are determined from an analysis of the NMR spectrum to be 〈 S
C
〉=1.63 and 〈S
D
〉=1.72.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 12, 988–993 (25 June 1998) 相似文献
16.
M. A. Zelikman 《Physics of the Solid State》1997,39(11):1751-1755
A system of pancake vortices formed near the boundary of a sample in a monotonically increasing external magnetic field is
calculated with allowance for pinning due to the cellular structure of the medium for various values of the pinning parameter
I, which is proportional to the critical current of the junction and the cell diameter. The shortest distance from the outermost
vortex to the nearest neighbor is proportional to I
−11. It is shown that the pinning parameter has a critical value I
c separating two regimes with different types of critical states. For I<I
c the external magnetic field has a threshold value H
t(I), above which the field immediately penetrates the interior of the junction to an infinite distance. For I>I
c the magnetic field decays linearly from the boundary into the interior of the junction. The value obtained in the study,
I
c=3.369, differs from the value of 0.9716 postulated by other authors. The dependence of the slope of the magnetic field profile
near the boundary on I is determined. It is shown that the slope is independent of I in intervals 2πk<I<2πk+π.
Fiz. Tverd. Tela (St. Petersburg) 39, 1958–1963 (November 1997) 相似文献
17.
I. F. Voloshin A. V. Kalinov L. M. Fisher K. I. Kugel’ A. L. Rakhmanov 《Journal of Experimental and Theoretical Physics》1997,84(6):1177-1185
Measurements of the imaginary part of the ac magnetic susceptibility of single crystals and melt-textured samples of YBa2Cu3Ox (YBCO) at T=77 K in a magnetic field ranging between 1 and 20 kOe are reported. If the dc magnetic field H
dc is rotated in the ab plane of the sample, the magnetic susceptibility and critical current density j
c have peaks corresponding to the magnetic field aligned with twin boundaries. Peaks in the curve of j
c versus magnetic field are observed at angles corresponding to these peaks, where
AH
dc in a wide range of magnetic fields. The results have been interpreted in terms of the theory describing twin boundaries as
a system of quasi-planar pinning sites. The pinning is strong if the elastic displacements of flux lines are of the order
of the vortex lattice constant d
f. These displacements decrease with the magnetic field because of the decrease in d
f, and the contribution of the elastic energy to the Gibbs potential is reduced accordingly, which is the cause of the peak
effect.
Zh. éksp. Teor. Fiz. 111, 2158–2174 (June 1997) 相似文献
18.
A. S. Borovik-Romanov S. V. Petrov A. M. Tikhonov B. S. Dumesh 《Journal of Experimental and Theoretical Physics》1998,86(1):197-205
The NMR spectrum of the quasi-one-dimensional easy-plane antiferromagnetic CsMnBr3, which has trigonal spin lattice, is investigated in detail. The measurements were performed on a wide-band NMR decimeter
microwave-band spectrometer over a wide range of magnetic fields at temperatures 1.3–4.2 K. All three branches of the NMR
spectrum previously found by us [JETP Lett. 64, 225 (1996)] are severely distorted because of the dynamic interaction with the Goldstone mode in the antiferromagnetic resonance
spectrum. The experimental results in fields up to 40 kOe are described satisfactorily by an equation obtained by Zaliznyak
et al. [JETP Lett. 64, 473 (1996)]. Formulas are obtained in our work that agree very well with experiment at all fields up to the “collapse” field
H
c
of all sublattices. The unbiased NMR frequency in CsMnBr3 is determined to be v
n0=416 MHz (T=1.3 K) in zero external magnetic field, and in this way the reduction in the spontaneous moment due to the quasi-one-dimensional
nature of the system of Mn2+ spins, which according to our data amounts to 28%, is determined more accurately. The field dependences of the directions
of the magnetic sublattices with respect to the magnetic field are obtained from the NMR spectra, confirming the equations
of Chubukov [J. Phys. Condens. Matter 21, 441 (1988)]. The results on the field dependence of the width and intensities of the NMR lines are discussed, along with
three observed anomalies: 1) a strong increase in the NMR frequency for nuclei in sublattices that are perpendicular to the
magnetic field; 2) the nonmonotonic temperature dependence of the resonance field for the lower branch of the spectrum; 3)
the presence of two branches of the NMR spectrum in large H
c
fields, in which the CsMnBr3 must be a quasi-one-dimensional antiferromagnetic.
Zh. éksp. Teor. Fiz. 113, 352–368 (January 1998)
Deceased. 相似文献
19.
In this article, we study the decays ψ′ → J/ψπ
+
π
− and η′c → η
c
π
+
π
− by taking into account the chiral symmetry breaking effects, the final-state interactions and the heavy-quark symmetry. We
can confront the predictions of the η′c → η
c
π
+
π
− decay width and differential decay width with the experimental data in the future, and obtain powerful constraints on the
chiral breaking effects and the final-state interactions, and test the heavy-quark symmetry. 相似文献
20.
The current-voltage characteristics of granular YBa2Cu3O6.95 high-temperature superconductor samples have been measured at a temperature of 77.3 K in external transverse magnetic fields
H
ext with a strength of up to H
ext ≈ 500 Oe for low transport current densities (0.1 A/cm2 ≤ j ≤ 0.6 A/cm2). The current-voltage characteristics obtained have been used to construct dependences of the magnetoresistance ρ on the
quantities j (ρ(j)
Hext=const) and H
ext(ρ(H
ext)
j = const). It has been revealed that the current and field dependences of the magnetoresistance exhibit anomalies at H
ext ≥ H
c1g
, where H
c1g
is the lower critical field of superconducting grains. A comparative analysis of the dependences ρ(j)H
ext = const and ρ(H
ext)
j = const has made it possible to develop concepts regarding the influence of the processes of redistribution of the magnetic field
between grain boundaries and superconducting grains on the transport and galvanomagnetic properties of granular high-temperature
superconductors. It has been established that the field dependences of the magnetoresistance exhibit specific features associated
with the beginning of penetration of Josephson vortices into grain boundaries in the magnetic field H
c1J
and with the breaking of a continuous chain of Josephson junctions in the magnetic field H
c2J
. 相似文献