共查询到20条相似文献,搜索用时 31 毫秒
1.
J.W. KimD.H. An S.K. ChangH.L. Ju K.S. BaekH.N. Oak H.S. Lee 《Journal of Physics and Chemistry of Solids》2002,63(2):241-247
CoFeRhO4 has been studied by Mössbauer spectroscopy and X-ray diffraction. The crystal is found to have a cubic spinel structure with the lattice constant a0=8.451±0.005 Å. The iron ions are in ferric states. The temperature dependence of the magnetic hyperfine field is analyzed by the Néel theory of ferrimagnetism. The intersublattice superexchange interaction is antiferromagnetic and strong with a strength of JAB=−12.39kB while the intrasublattice superexchange interactions are weak with strengths of JAA=−4.96kB and JBB=6.20kB. As the temperature increases toward the Néel temperature TN, a systematic line broadening effect in the Mössbauer spectrum is observed and interpreted to originate from different temperature dependences of the magnetic hyperfine fields at various iron sites. 相似文献
2.
3.
Junfeng Sun Dongsheng Du Yueling Yang 《The European Physical Journal C - Particles and Fields》2009,60(1):107-117
The B
c
→J/ψ
π, η
c
π decays are studied with the perturbative QCD approach. It is found that the form factors
and
for the B
c
→J/ψ, η
c
transitions and the branching ratios are sensitive to the parameters ω, v, f
J/ψ
and
, where ω and v are the parameters of the charmonium wave functions for a Coulomb potential and the harmonic-oscillator potential, respectively,
and f
J/ψ
and
are the decay constants of the J/ψ and η
c
mesons, respectively. The large branching ratios and the clear signals of the final states make the B
c
→J/ψ
π, η
c
π decays the prospective channels for measurements at the hadron colliders. 相似文献
4.
A. K. Chaudhuri 《The European Physical Journal C - Particles and Fields》2009,61(2):331-338
In a hydrodynamic model, we have studied J/ψ production in Au+Au/Cu+Cu collisions at RHIC energy,
GeV. At the initial time, J/ψ’s are randomly distributed in the fluid. As the fluid evolves in time, the free streaming J/ψ’s are dissolved if the local fluid temperature exceeds a threshold temperature T
J/ψ
. Sequential melting of charmonium states (χ
c
, ψ
′ and J/ψ), with melting temperatures
, T
J/ψ
≈2T
c
and feed-down fraction F≈0.3, explains the PHENIX data on the centrality dependence of J/ψ suppression in Au+Au collisions. J/ψ
p
T
spectra and the nuclear modification factor in Au+Au collisions are also well explained in the model. The model however overpredicts
the centrality dependence of J/ψ suppression in Cu+Cu collisions by 20–30%. The J/ψ
p
T
spectra are underpredicted by 20–30%. The model predicts that in central Pb+Pb collisions at LHC energy,
GeV, J/ψ’s are suppressed by a factor of ∼10. The model predicted a J/ψ
p
T
distribution in Pb+Pb collisions at LHC is similar to that in Au+Au collisions at RHIC. 相似文献
5.
K. Koizumi M. Shoji Y. Kitagawa H. Ohoyama T. Kasai K. Yamaguchi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(1):193-197
The electronic structure and effective exchange integrals (J ab)
between two manganese (III) ions of porphyrin dimer (PPMn(III)–OH–Mn(III)PP)
were examined by using unrestricted hybrid DFT (UHDFT) methods. The
dependence of Jab on bond angle between two manganese (
Mn–OH–Mn) is
also calculated to elucidate orbital overlap effect for Jab value in the system. Natural orbital analysis is performed to explain the overlap effect in terms of the instability of the
π, σ and δ orbitals by using diradical character. 相似文献
6.
Beno?t?Collins Kenneth?J.?Dykema Francisco?Torres-Ayala 《Journal of statistical physics》2010,139(5):779-799
We show that the polynomial S
m,k
(A,B), that is the sum of all words in noncommuting variables A and B having length m and exactly k letters equal to B, is not equal to a sum of commutators and Hermitian squares in the algebra R〈X,Y〉, where X
2=A and Y
2=B, for all even values of m and k with 6≤k≤m−10, and also for (m,k)=(12,6). This leaves only the case (m,k)=(16,8) open. This topic is of interest in connection with the Lieb–Seiringer formulation of the Bessis–Moussa–Villani conjecture,
which asks whether Tr (S
m,k
(A,B))≥0 holds for all positive semidefinite matrices A and B. These results eliminate the possibility of using “descent + sum-of-squares” to prove the BMV conjecture. 相似文献
7.
M. Lengen E. Bill C. Butzlaff A. X. Trautwein M. Winter P. Chaudhuri 《Hyperfine Interactions》1994,94(1):1849-1853
The magnetic properties of [L-Fe(III)-dmg3Mn(II)-Fe(III)-L] (ClO4)2 have been characterized by magnetic susceptibility, EPR, and Mössbauer studies. L represents 1,4,7-trimethyl-, 1,4,7-triazacyclononane and dmg represents dimethylglyoxime. X-ray diffraction measurements yield that the arrangement of the three metal centers is strictly linear with atomic distancesd
Fe-Mn=0.35 nm andd
Fe-Fe=0.7 nm. Magnetic susceptibility measurements (3–295 K) were analyzed in the framework of the spin-Hamiltonian formalism considering Heisenberg exchange and Zeeman interaction:=J
Fe-Mn(S
Fe1+S
Fe2)S
Mn +J
Fe-Fe(S
Fe1
S
Fe2) +gB
S
total
B. The spinsS
Fe1=S
Fe2 =S
Mn=5/2 of the complex are antiferromagnetically coupled, yielding a total spin ofS
total=5/2 with exchange coupling constantsF
Fe-Mn=13.4 cm–1 andJ
Fe-Fe= 4.5 cm–1. Magnetically split Mössbauer spectra were recorded at 1.5 K under various applied fields (20 mT, 170 mT, 4T). The spin-Hamiltonian analysis of these spectra yields isotropic magnetic hyperfine coupling withA
total/(g
N
N)=–18.5 T. The corresponding local componentA
Fe is related toA
total via spin-projection:A
total=(6/7)AFe. The resultingA
Fe/(g
NN)=–21.6 T is in agreement with standard values of ferric high-spin complexes. Spin-Hamiltonian parameters as obtained from Mössbauer studies and exchange coupling constants as derived from susceptibility measurements are corroborated by temperature-dependent EPR studies. 相似文献
8.
We calculate high-temperature graph expansions for the Ising spin glass model with 4 symmetric random distribution functions for its nearest neighbor interaction constants J
ij
. Series for the Edwards-Anderson susceptibility
are obtained to order 13 in the expansion variable (J/(k
B
T))2 for the general d-dimensional hyper-cubic lattice, where the parameter J determines the width of the distributions. We explain in detail how the expansions are calculated. The analysis, using the Dlog-Padé approximation and the techniques known as M1 and M2, leads to estimates for the critical threshold (J/(k
B
T
c
))2 and for the critical exponent
in dimensions 4, 5, 7 and 8 for all the distribution functions. In each dimension the values for
agree, within their uncertainty margins, with a common value for the different distributions, thus confirming universality.Received: 22 July 2004, Published online: 12 October 2004PACS:
05.70.Jk Critical point phenomena - 75.10.Nr Spin-glass and other random models 相似文献
9.
M. Hansmann 《Mathematical Physics, Analysis and Geometry》2007,10(3):261-270
We derive new bounds on the moments of the negative eigenvalues of a selfadjoint operator B. The moments of order are estimated in terms of Schatten-norm bounds on the difference of the semigroups generated by B and a reference operator A which is assumed to be nonnegative and selfadjoint. The estimate in the case γ = 1 is sharp.
相似文献
10.
11.
12.
S.A. Blundell M.D. Núñez-Regueiro 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):453-456
From the recently determined structure of the delafossite YCuO2.5, we argue that the Cu-O network has nearly independent Δ chains but with different interactions between the s = 1/2 spins. Motivated by this observation, we study the Δ chain for different ratios of the base-base and base-vertex interactions,
J
bb/J
bv. By exact diagonalization and extrapolation, we show that the elementary excitation spectrum is the same for total spins
S
tot = 0 and 1, but not for S
tot = 2, and has a gap only in the interval 0.4874(1) ⩽ J
bb/J
bv ⩽ 1.53(1). The gap, known to be dispersionless for J
bb = J
bv, is found to acquire increasing k-dependence as J
bb/J
bv moves away from unity.
Received 29 October 2002 / Received in final form 14 January 2003 Published online 6 March 2003
RID="a"
ID="a"e-mail: sblundell@cea.fr
RID="b"
ID="b"e-mail: nunezreg@lps.u-psud.fr 相似文献
13.
S. V. Mel’nichuk Ya. M. Mikhailevskii A. I. Savchuk D. N. Trifonenko 《Physics of the Solid State》1997,39(2):301-304
The superexchange interaction integral J
NN is investigated in semimagnetic semiconductors of the type A
1−x
II
MxBVI systems, where the Mn, Fe, and Co ions are considered as the magnetic component M. Calculations are done in the framework
of Racah’s many particle theory including the ground orbital states of the M ions in a cubic crystal. The results of these
calculations are compared with published experimental data and with data from a study of the temperature dependence of Faraday
rotation. The superexchange mechanism can be used to explain the correlation in the critical values x* at which the interionic interaction becomes important for the Cd1−x
MnxTe and Cd1−x
FexTe systems.
Fiz. Tverd. Tela (St. Petersburg) 39, 344–348 (February 1997) 相似文献
14.
15.
J/ψ production at forward and midrapidity at the Relativistic Heavy-Ion Collider (RHIC) is calculated within a previously constructed
rate-equation approach accounting for both direct production and regeneration from c and
. The results are compared to the experimental data. The observed stronger suppression at forward rapidity can be qualitatively
explained by a smaller statistical regeneration component together with stronger cold nuclear matter induced suppression compared
to midrapidity. The χ
c
over J/ψ ratio and ψ′ over J/ψ ratio are also calculated. 相似文献
16.
A. I. Parkhomenko 《Journal of Experimental and Theoretical Physics》1999,88(5):913-920
The sudden approximation in energy is used to derive analytic formulas that describe the anomalous light-induced drift (LID)
of linear molecules absorbing radiation in the rovibrational transition nJ
i
−mJ
f
(n and m are the ground and excited vibrational states, and J
α
is the rotational quantum number in the vibrational state α=m, n). It is shown that for all linear molecules with moderate values B≲1 cm−1 of the rotational constant, anomalous LID can always by observed under the proper experimental conditions; temperature T, rotational quantum number J
i
, and type of transition (P or R). The parameter γ=B[J
i
(J
i
+1)−J
f
(J
f
+1)] ν
n
/2k
BT
(ν
m
−ν
n
) is used to derive a condition for observing anomalous LID: γ∼1 (k
B
is the Boltzmann constant and ν
α
is the transport rate of collisions of molecules in the vibrational state α and buffer particles at moderate molecular velocities
, where
is the most probable velocity of the buffer particles). For ν
m
>ν
n
anomalous LID can be observed only in P-transitions, while for ν
m
<ν
n
it can be observed only in R-transitions. It is shown that anomalous LID is possible for all ratios β=M
b
/M of the masses of the buffer particles (M
b
) and of the resonant particles (M) and any absorption-line broadening (Doppler or homogeneous). The optimum conditions for observing anomalous LID are realized
when the absorption line is Doppler-broadened in an atmosphere of medium-weight (β∼1) and heavy (β≫1) buffer particles. In this case, anomalous LID can be observed in the same transition within a broad temperature interval
ΔT∼T. If the buffer particles are light (β≪1) or if the broadening of the absorption line is homogeneous, anomalous LID in the same transition can be observed only
within a narrow temperature range ΔT≪T.
Zh. éksp. Teor. Fiz. 115, 1664–1679 (May 1999) 相似文献
17.
We analyze the ferromagnetic Ising model on non-Euclidean scale invariant lattices with aperiodic interactions (JA,JB,JC,JD) defined by Rudin-Shapiro substitution rules with Migdal-Kadanoff renormalization (MKR) and transfer matrix (TM) techniques. The analysis of the invariant sets of the zero-field MKR transformation indicates that the critical behavior, completely distinct from the one of the uniform model, is described by a new off-diagonal fixed point. This contrasts with other aperiodic models where the new critical behavior is described by a period-two cycle. With the new fixed point, values for the thermal critical exponents,
and
, as well as the period of log-periodic oscillations, are obtained. Exact recursive maps for all thermodynamical functions are derived within the TM approach. The explicit dependence of the thermodynamical functions with respect to temperature is evaluated by the numerical iteration of the set of maps until a previously chosen convergence is achieved. They also indicate that, depending on the actual choice for the aperiodic coupling constants, the magnetic exponents (
and
) assume different values. However the Rushbrook relation is always satisfied.Received: 27 February 2003, Published online: 11 August 2003PACS:
05.50.+q Lattice theory and statistics -
05.10.Cc Renormalization group methods -
64.60.Ak Renormalization-group, fractal, and percolation studies of phase
transitions -
61.44.Br Quasicrystals 相似文献
18.
We study the inflated phase of two dimensional lattice polygons with fixed perimeter N and variable area, associating a weight exp [pA−Jb] to a polygon with area A and b bends. For convex and column-convex polygons, we calculate the average area for positive values of the pressure. For large
pressures, the area has the asymptotic behaviour
, where
, and ρ<1. The constant K(J) is found to be the same for both types of polygons. We argue that self-avoiding polygons should exhibit the same asymptotic
behavior. For self-avoiding polygons, our predictions are in good agreement with exact enumeration data for J=0 and Monte Carlo simulations for J≠0. We also study polygons where self-intersections are allowed, verifying numerically that the asymptotic behavior described
above continues to hold. 相似文献
19.
S. S. Aplesnin 《Physics of the Solid State》1999,41(1):103-107
The two-dimensional (2D) Heisenberg model with anisotropic exchange (Δ = 1−J
x
/J
z
) and S=1/2 is investigated by the quantum Monte Carlo method. The energy, susceptibility, specific heat, spin-spin correlation functions,
and correlation radius are calculated. The sublattice magnetization (σ) and the Néel temperature of the anisotropic antiferromagnet are logarithmic functions of the exchange anisotropy: 1/σ+1+0.13(1)ln(1/Δ). Crossover of the static magnetic structural factor as a function of temperature from power-law to exponential
occurs for T
c
/J≈0.4. The correlation radius can be approximated by 1/ξ=2.05T
1.0(6)/exp(1.0(4)/T). For La2CuO4 the sublattice magnetization is calculated as σ=0.45, the exchange is J=(1125–1305) K; for Er2CuO4
J∼625 K and the exchange anisotropy Δ∼0.003. The temperature dependence of the static structural magnetic factor and the correlation
radius above the Néel temperature in these compounds can be explained by the formation of topological excitations (spinons).
Fiz. Tverd. Tela (St. Petersburg) 41, 116–121 (January 1999) 相似文献
20.
Let a<b,
and H be the (formal) Hamiltonian defined on Ω by
where J:ℤ
d
→ℝ is any summable non-negative symmetric function (J(x)≥0 for all x∈ℤ
d
, ∑
x
J(x)<∞ and J(x)=J(−x)). We prove that there is a unique Gibbs measure on Ω associated to H. The result is a consequence of the fact that the corresponding Gibbs sampler is attractive and has a unique invariant measure. 相似文献
(1) |