共查询到20条相似文献,搜索用时 15 毫秒
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2.
Within the differential operator method and the effective-field approximation, the critical behaviour of the amorphous Ising ferromagnet with a random field is studied. Tricritical points and reentrant phenomena are discussed. The influence of the random field and the amorphization on the transition temperature is also investigated. 相似文献
3.
We compute the exact partition function of 2d Ising spin glasses with binary couplings. In these systems, the ground state is highly degenerate and is separated from the first excited state by a gap of size 4J. Nevertheless, we find that the low temperature specific heat density scales as exp(-2J/T), corresponding to an "effective" gap of size 2J; in addition, an associated crossover length scale grows as exp(J/T). We justify these scalings via the degeneracy of the low lying excitations and by the way low energy domain walls proliferate in this model. 相似文献
4.
We report the Bose-Einstein condensation (BEC) of the most magnetic element, dysprosium. The Dy BEC is the first for an open f-shell lanthanide (rare-earth) element and is produced via forced evaporation in a crossed optical dipole trap loaded by an unusual, blue-detuned and spin-polarized narrowline magneto-optical trap. Nearly pure condensates of 1.5 × 10(4) (164)Dy atoms form below T = 30 nK. We observe that stable BEC formation depends on the relative angle of a small polarizing magnetic field to the axis of the oblate trap, a property of trapped condensates only expected in the strongly dipolar regime. This regime was heretofore only attainable in Cr BECs via a Feshbach resonance accessed at a high-magnetic field. 相似文献
5.
Freeman J. Dyson 《Communications in Mathematical Physics》1969,12(2):91-107
Existence of a phase-transition is proved for an infinite linear chain of spins μ j =±1, with an interaction energy $$H = - \sum J(i - j)\mu _i \mu _j ,$$ whereJ(n) is positive and monotone decreasing, and the sums ΣJ(n) and Σ (log logn) [n 3 J(n)]?1 both converge. In particular, as conjectured byKac andThompson, a transition exists forJ(n)=n ?α when 1 < α < 2. A possible extension of these results to Heisenberg ferromagnets is discussed. 相似文献
6.
Magnetic properties (magnetization curve, magnetization process, specific heat and paramagnetic susceptibility) of a diluted spin-
Ising ferromagnet on a honeycomb lattice are examined by the use of the new formulation based on both the Ising spin identities and the differential operator technique. We find a number of characteristic phenomena, for the system with a negative value of the crystal-field constant in the special region. The physical background is also discussed. 相似文献
7.
We have discovered two novel aspects of the stripe-domain to paramagnetic transition in perpendicularly magnetized Fe films on Cu(100). First, the width of the stripes carrying oppositely oriented spins decreases, close to the transition temperature, with a power law. Second, in a small temperature interval close to the transition temperature, the stripes--which form stationary patterns at low temperatures--become mobile. Various theoretical works have predicted stripe mobility in similar frustrated systems but no direct proof of this phenomenon has been reported so far. 相似文献
8.
A. Ojo 《Physics letters. A》1973,45(4):313-314
By calculating the partition function over all one-break configurations the transition temperature of a one-dimensional Ising ferromagnet, with inverse-square interaction, is determined. 相似文献
9.
D. B. Abraham 《Journal of statistical physics》1978,19(4):349-358
The critical index values= 7/4 for the susceptibility and=15 for the critical isotherm are derived rigorously for the rectangular Ising ferromagnet with nearest neighbor interactions. The critical indices associated with the Fisher moment definition of the correlation length are obtained asTT
c+. The index of the fluctuation sum definition of critical correlations is obtained.Partially supported by grant PHY 76 17191. 相似文献
10.
Hase M. O. de Almeida J. R.L. Salinas S. R. 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,47(2):245-249
We use the replica method in order to obtain an expression for the
variational free energy of an Ising ferromagnet on a Viana-Bray lattice in
the presence of random external fields. Introducing a global order
parameter, in the replica-symmetric context, the problem is reduced to the
analysis of the solutions of a nonlinear integral equation. At zero
temperature, and under some restrictions on the form of the random fields,
we are able to perform a detailed analysis of stability of the
replica-symmetric solutions. In contrast to the behaviour of the
Sherrington-Kirkpatrick model for a spin glass in a uniform
field, the paramagnetic solution is fully stable in a sufficiently large
random field. 相似文献
11.
We report the time-dependent nucleation fluxes and associated nucleation rates in a metastable Ising ferromagnet on square lattice with Metropolis (Glauber-type) dynamics. It is discovered that, with lowering of the temperature, fluxes collapse into several representative transient curves corresponding to magic cluster sizes. Those can be associated with physical droplets, i.e., long-lived configurations which provide a link with the classical Becker-D?ring picture. 相似文献
12.
The parallel magnetic susceptibility χ of a uniaxial ferromagnet ErCl3·6H2O has been measured between 0.3 and 4.2K and specially near Tc = 0.353 K. The predominant contribution to the Curie-Weiss temperature is due to the dipolar interactions. χ is proportional to ??γ with in the range 10?3 < ? < 5 × 10?2. The γ value, γ = 1.01 ±0.03 is consistent with the theoretical prediction for a uniaxial dipolar ferromagnet. 相似文献
13.
V.N. Kashcheev 《Physics letters. A》1976,57(4):375-376
Under general assumptions about the magnon dispersion for the model quoted in the title it is stated that at low temperatures T the specific heat is linear in T and the susceptibility is proportional to exp(const/T). 相似文献
14.
Within the framework of an effective-field approximation, we calculate the magnetization, specific heat and susceptibility of a quenched site-bond diluted Ising ferromagnet in honeycomb lattice as the functions of site and bond concentrations. These results have a substantial improvement over the standard molecular field approximation. 相似文献
15.
The method of averaging over the exchange interaction fields has been considered as applied to clusters of one and two magnetic atoms in the Ising model of a dilute ferromagnet, and a variant of fixed-scale group renormalization on the basis of this method has been constructed. It has been shown that the approximation obtained makes it possible to distinguish models with the site and bond dilutions. 相似文献
16.
Magnetization measurements on GdCl3, a 3-dimensional ferromagnet (Tc = 2.2105 K) with a weak isotropic Heisenberg exchange and dipole-dipole interactions of the same order of magnitude, yield crititcal exponents of β = 0.418 ± 0.007, γ = 1.078 ± 0.01, δ = 3.53 ± 0.05. They satisfy Widom's equality β(δ - 1) = γ but differ appreciably from values of systems with dominating short-range interactions. The results are compared with theories of larkin et al. (1969) and Fischer et al. (1972) for ferromagnets with long-range interactions. 相似文献
17.
《Journal of magnetism and magnetic materials》2005,295(1):57-64
A Green's function formalism is used to calculate the spectrum of excitations of two neighboring impurities implanted in a semi-infinite ferromagnetic. The equations of motion for the Green's functions are determined in the framework of the Ising model in a transverse field and results are given for the effect of the exchange coupling, position and orientation of the impurities on the spectra of localized spin wave modes. 相似文献
18.
Tom Hosiawa 《Journal of magnetism and magnetic materials》2009,321(12):1878-1884
Magnetic domain structures are a fascinating area of study with interest deriving both from technological applications and fundamental scientific questions. The nature of the striped magnetic phases observed in ultra-thin films is one such intriguing system. The non-equilibrium dynamics of such systems as they evolve toward equilibrium has only recently become an area of interest and previous work on model systems showed evidence of complex, slow dynamics with glass-like properties as the stripes order mesoscopically. To aid in the characterization of the observed phases and the nature of the transitions observed in model systems we have developed an efficient method for identifying clusters or domains in the spin system, where the clusters are based on the stripe orientation. Thus we are able to track the growth and decay of such clusters of stripes in a Monte Carlo simulation and observe directly the nature of the slow dynamics. We have applied this method to consider the growth and decay of ordered domains after a quench from a saturated magnetic state to temperatures near and well below the critical temperature in the 2D dipolar Ising model. We discuss our method of identifying stripe domains or clusters of stripes within this model and present the results of our investigations. 相似文献
19.
In zero magnetic field susceptibility, magnetization and specific heat of GdCl3 follow below t = |T/Tc - 1| ≈0.015 mean field laws with logarithmic corrections. Their amplitudes characterizing the strengths of the singularities are related by an equation predicted by the theory of Larkin and Khmel'nitzkii. 相似文献
20.
The high-field magnetization for the amorphization of a Ising ferromagnet in a square lattice is investigated. The exchange parameters are assumed to have a delta function distribution. From the examination of the approach of magnetization to saturation, some informations about the structural inhomogeneities in the amorphization are obtained. 相似文献