共查询到20条相似文献,搜索用时 156 毫秒
1.
Hai-Jun Wang Yuan Chen Liang-Jie Fu Rui-Na Lin Chuang-Chuang Song 《Journal of magnetism and magnetic materials》2009,321(12):1904-1908
One-dimensional single-ion anisotropic ferromagnet with spin-1 is investigated by means of Green's function treatment in this paper. The model Hamiltonian includes a Heisenberg ferromagnetic term, an external magnetic field, and a second-order single-ion anisotropy. The magnetic properties of the system are treated by the random phase approximation for the exchange interaction term and the Anderson-Callen approximation for the anisotropy term. Our paramagnetic results are in agreement with the other theoretical results. 相似文献
2.
The spin-1/2 quantum Heisenberg ferromagnet with anisotropic spin exchange interactions in three dimensions are investigated by means of the Green's function method.
In the Tyablikov approximation, the correlation functions,
the magnetization, and the susceptibilities are computed.
The magnetic properties of this model are found to be dependent of anisotropy. 相似文献
3.
A quantum Ising-like spin-1 model characterized by quadrupolar interaction, coupled to an external anisotropic field with both dipole and quadrupole momenta is analyzed. The general phase diagram (including temperature), as well as order parameter, specific heat, and susceptibility are evaluated in the mean-field approximation and exibit a rich structure with transitions of 2° and 1° order and tricritical points. ForT=0 the phase diagram is examined also by a recently formulated improved version of mean-field theory which has the usual mean-field theory as its zero-th order approximation. 相似文献
4.
We study the linear anisotropic spin-1/2-Heisenberg model with periodic as well as antiperiodic boundary conditions. Using two assumptions about the eigenvalues of the related fermion models it is shown, how the exactly known energy spectrum of the periodic Heisenberg model is altered in the antiperiodic case. This investigation provides basis for a subsequent test of a Hartree-Fock approximation. It gives fairly good results for the groundstate energy and the energy dispersion of low-lying excitations. Hartree-Fock solutions with gapless excitations yield a qualitatively correct picture of the phase diagram of the Heisenberg model. 相似文献
5.
CHEN Yuan XIANG Ying HU Ai-Yuan 《理论物理通讯》2008,49(5):1349-1352
Longitudinal susceptibility of the spin-1/2 low-dimensional Heisenberg ferromagnet in a magnetic field, is
studied by the Green's function method within the random phase
approximation. The static and dynamic longitudinal susceptibilities
are calculated in the low- and high-field regions. Power laws for
the position and height of the static susceptibility maximum are
shown not to support the predictions of Landau theory. 相似文献
6.
L. Campos Venuti C. Degli Esposti Boschi E. Ercolessi G. Morandi F. Ortolani S. Pasini M. Roncaglia 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(1):11-18
Motivated by field-theoretic predictions we investigate the stable
excitations that exist in two characteristic gapped phases of a spin-1
model with Ising-like and single-ion anisotropies. The sine-Gordon
theory indicates a region close to the phase boundary where a stable
breather exists besides the stable particles, that form the Haldane
triplet at the Heisenberg isotropic point. The numerical data, obtained
by means of the Density Matrix Renormalization Group, confirm this
picture in the so-called large-D phase for which we give also a
quantitative analysis of the bound states using standard perturbation
theory. However, the situation turns out to be considerably more intricate
in the Haldane phase where, to the best of our data, we do not observe
stable breathers contrarily to what could be expected from the sine-Gordon
model, but rather only the three modes predicted by a novel anisotropic
extension of the Non-Linear Sigma Model studied here by means of a
saddle-point approximation. 相似文献
7.
AST Pires 《Zeitschrift für Physik B Condensed Matter》1995,97(4):553-557
We discuss the use of the self consistent harmonic approximation applied to the two-dimensional classical anisotropic Heisenberg ferromagnet. The Kosterlitz-Thouless transition temperature for the isotropic antiferromagnet in a uniform magnetic field, applied perpendicular to the xy plane, is obtained. 相似文献
8.
Yu.A. Fridman D.A. Matunin Ph.N. Klevets O.A. Kosmachev 《Journal of magnetism and magnetic materials》2009,321(22):3782-3794
The phase states of the 2D non-Heisenberg ferromagnetic with anisotropic bilinear and biquadratic exchange interactions are investigated. The limiting cases of the system under consideration are the two-dimensional XY-model with biquadratic exchange interaction and the isotropic Heisenberg ferromagnetic. The account of the magnetic dipole interaction leads to the realization of spatially inhomogeneous quadrupolar phase. The stability regions of various phase transitions for different values of the material parameters are studied. The phase diagram is built. Besides, the temperature phase transitions are investigated. The influence of the magnetoelastic interaction on the formation of the long-range quadrupolar order is determined. 相似文献
9.
自旋s=1的海森堡反铁磁链材料LiVGe2O6的磁化率以及 核磁共振实验表明该材料在临界温度约为22 K时由顺磁相转变为反铁磁Néel相, 且低温磁激发谱存在能隙. 本文在已有模型哈密顿量的基础上提出了一个低能场论模型——Ginzburg-Landau理论来描述 这一反铁磁链材料, 并运用这一理论讨论了LiVGe2O6由于自发对称性破缺导致的有限温度相变及 相应的磁化率变化情况, 理论计算很好地解释了现有的实验结果.
关键词:
海森堡模型
σ模型')" href="#">O(3)非线性σ模型
有限温度相变 相似文献
10.
Instability of the excitation spectrum of an ordered noncollinear Heisenberg antiferromagnet with respect to spontaneous two-magnon decays is investigated. We use a spin-1/2 antiferromagnet on a triangular lattice as an example and examine the characteristic long- and short-wavelength features of its zero-temperature spectrum within the 1/S approximation. The kinematic conditions are shown to be crucial for the existence of decays and for overall properties of the spectrum. The XXZ and the J-J generalizations of the model, as well as the role of higher-order corrections, are discussed. 相似文献
11.
R. R. Levitskii O. R. Baran B. M. Lisnii 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(3):439-443
The spin-1 Ising model with bilinear and quadrupolar short-range
interactions under magnetic field is investigated within the
two-particle cluster approximation. It is shown that for those
values of the quadrupolar interaction when at zero magnetic field
the system undergoes a temperature phase transition between
quadrupolar and paramagnetic phases, a triple point may exist in
the temperature vs. magnetic field phase diagrams, necessarily
along with a critical point. It is also shown that the critical
points in the temperature vs. magnetic field phase diagrams of the
investigated model can be of three types. 相似文献
12.
13.
The spin-1/2 anisotropic Heisenberg model is studied by generalizing the Migdal-Kadanoff renormalization transformations to quantum spin systems. An approximate one-dimensional decimation is employed besides the potential-moving approximation in this generalization. It is shown that these approximations are valid at high temperatures. The results obtained from these approximations suggest that the two-dimensional spin-1/2X-Y model shows the critical behavior similar to that expected for the classicalX-Y and planar models. 相似文献
14.
Girardeau MD 《Physical review letters》2006,97(21):210401
The ground and excited states of a one-dimensional (1D) spin-1/2 Fermi gas (SFG) with both attractive zero-range odd-wave interactions and repulsive zero-range even-wave interactions are mapped exactly to a 1D Lieb-Liniger-Heisenberg (LLH) model with delta-function repulsions depending on isotropic Heisenberg spin-spin interactions, such that the complete SFG and LLH energy spectra are identical. The ground state in the ferromagnetic phase is given exactly by the Lieb-Liniger (LL) Bethe ansatz, and that in the antiferromagnetic phase by a variational method combining Bethe ansatz solutions of the LL and 1D Heisenberg models. There are excitation branches corresponding to LL type I and II phonons and spin waves, the latter behaving quadratically for small wave numbers in the ferromagnetic phase and linearly in the antiferromagnetic phase. 相似文献
15.
16.
The method of equations of motion for spin operators in the case of O(3) Heisenberg ferromagnet is systematically analyzed starting from the effective Lagrangian. It is shown that the random phase approximation and the Callen approximation can be understood in terms of perturbation theory for type B magnons. Also, the second order approximation of Kondo and Yamaji for one dimensional ferromagnet is reduced to the perturbation theory for type A magnons. An emphasis is put on the physical picture, i.e. on magnon–magnon interactions and symmetries of the Heisenberg model. Calculations demonstrate that all three approximations differ in manner in which the magnon–magnon interactions arising from the Wess–Zumino term are treated, from where specific features and limitations of each of them can be deduced. 相似文献
17.
Lincoln Stoller 《International Journal of Theoretical Physics》1987,26(8):805-826
Monte Carlo techniques are used to show that a free-spin-wave theory of the quantum Heisenberg spin-1/2 ferromagnet, formulated to accurately represent the state space of the underlying system, predicts the critical temperature of the interacting theory to within 1% and critical exponents to within a factor of two. 相似文献
18.
By means of the dynamical vertex approximation (DΓA) we include spatial correlations on all length scales beyond the dynamical mean-field theory (DMFT) for the half-filled Hubbard model in three dimensions. The most relevant changes due to nonlocal fluctuations are (i) a deviation from the mean-field critical behavior with the same critical exponents as for the three dimensional Heisenberg (anti)ferromagnet and (ii) a sizable reduction of the Néel temperature (T(N)) by ~30% for the onset of antiferromagnetic order. Finally, we give a quantitative estimate of the deviation of the spectra between DΓA and DMFT in different regions of the phase diagram. 相似文献
19.
最近Frydman等人报道了联合MAS及多量子方法获取半整数四极核各向同性谱的新途径,本文以自旋3/2的四极核为例,采用步进式时序积分手续,数值计算了魔角样品旋转条件下的传播子,从而真实地模拟了非对易含时Hamiltonian情况下的密度矩阵演化;对Fryman等人采用的双脉冲序列实验应采取的最佳条件进行了详尽的理论分析;并对Na2C2O4样品的2D-MQ-MAS实验进行拟谱。 相似文献
20.
The existence is shown of bound complexes of three magnons in a two-dimensional simple cubic Heisenberg ferromagnet. The Heisenberg spin hamiltonian is replaced by Dyson's boson hamiltonian. The spurious features of this hamiltonian are treated explicitly. Using Faddeev's formalism, detailed calculations of the three-magnon bound state energy curves have been performed both for the isotropic and the longitudinally anisotropic ferromagnet. Attention is paid to the possibility of observing these three-magnon bound states experimentally. 相似文献