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1.
At T=2°K, a magnon and a phonon Raman line is observed respectively at 38.5 and 56.7 cm?1. The last one arises from an acoustic phonon at R point in the paramagnetic Brillouin zone, coupled to the magnon in the magnetically ordered phase.  相似文献   

2.
We report results of far infrared magneto-absorption experiments in FeBr2 doped with 1% MnBr2. Using radiations from several carcinotrons covering the frequency range 77–600 GHz, we observe both the spectra corresponding to the localized Mn2+ impurity modes and the uniform magnon modes of the host crystal. The excitation energy gap of the A.F. magnons at zero field is Eo = 500 ± 2 GHz.  相似文献   

3.
Raman scattering by phonons and by magnon pairs has been observed in Fe3BO6. Of the predicted 60 Raman-active modes, 39 have been identified and classified according to their symmetries. The two-magnon band shows a strong decrease in intensity with increasing temperature, and almost vanishes close to TN = 508 K. The origin of this effect is attributed to the existence of a nearly dispersionless magnon branch.  相似文献   

4.
T. Datta 《Physics letters. A》1984,103(5):243-246
A magnetic monopole moving faster than the magnon phase velocity in a given magnetic medium will create a magnon Cherenkov radiation in this medium. Typical velocities of interest are in the ~10?4c range. In this range most non-induction detection mechanisms are inefficient.  相似文献   

5.
The magnon energy bands are studied for a four-layer ferromagnetic superlattice, with regard to the effects of the competition between the anisotropy and the spin quantum number. A special attention is also paid on the effects of the symmetry of the system. It is found that three modulated energy gaps exist in the magnon energy band along Kx direction perpendicular to the superlattice plane. The magnetic anisotropy affects significantly the magnon energy gaps. The zero energy gap Δω23 correlates with the conditions between anisotropy constants, D1+D3=D2+D4 and D1=D3 (or D2=D4), while the disappearance of the magnon energy gaps Δω12 and Δω34 corresponds to a translational symmetry of x-direction in a unit cell. When the parameters of the system deviate from these conditions, the energy gaps Δω12, Δω23 and Δω34 become larger. There is a competition effect of the anisotropy and the spin quantum number on the magnon energy gaps Δω12 and Δω23. When the symmetry of the system is higher, the competition can achieve a balance to cause the zero energy gap.  相似文献   

6.
The interaction between magnons and photons which is responsible for magnetic polariton formation is expressed in terms of second quantized operators, and it is confirmed that the polariton dispersion curve obtained by diagonalizing the Hamiltonian is the same as that found classically. A term describing relaxation of the polariton by the two magnon mechanism which is often dominant in ferromagnetic resonance is then introduced. The lineshape function for inelastic light scattering is calculated by a Greens function technique. On the assumption that the lineshape can be approximated as a Lorentzian an expression for the linewidth is derived. The linewidth is zero when the polariton frequency Ω lies outside the magnon manifold, and increases discontinuously from zero at w = ¦γ¦H0, where H0 is the (internal) static field.  相似文献   

7.
The coherent quantum state of magnons—Bose–Einstein condensate (BEC) has been observed in several types of antiferromagnets. According to the Bose statistics of magnons, BEC appears when the magnon density exceeds the critical density N BEC and the magnon gas condenses to a quantum liquid. The BEC state is characterized by a coherent precession of the magnetization. In this paper, the first experiments showing the suppression of the spin echo signal by the magnon BEC is presented. These experiments confirm the coherence of magnetic excitations in the BEC state.  相似文献   

8.
We report on Raman scattering from the magnons in CsCoCl3 with particular emphasis on two magnetic phase transitions occurring at TN = 20.82 K and at 8 K. The T → 0 magnon spectrum is fitted by a S = 12 anisotropic Heisenberg model. With a simple cluster model we can explain the temperature behaviour of the magnon frequencies and intensities. The physics of the 8 K phase transition is also discussed.  相似文献   

9.
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   

10.
We consider an idealized model, represented by a Heisenberg spin system, which is influenced by a narrow conduction band via ans-d-exchange interaction. By calculating and decoupling the equation of motion of double-time Green's functions by RPA, we derive the magnon dispersion law. The result is a separation of the spectrum into two magnon bands of different shape, similar to the band structure found by Hubbard in his system. We discuss our result by variation of the system parameters, as there are interactions, polarization, temperature, and external field.  相似文献   

11.
The anisotropic exchange interaction between localized spins and conduction electrons is described by an appropriate spin hamiltonian. This is used to calculate the lifetime of magnons for arbitrary values of Λeq, where Λe is the electron mean free path and q the magnon wavevector. At Λeq ? 1, this lifetime depends on the angle between q and the saturation magnetization. The antisymmetric part of anisotropic exchange (Dzialoshinsky-Moriya interaction) may dominate the relaxation of spin-waves of large q. The complicated band structure of transition metals gives rise to a magnon lifetime independent of Λe. The contribution of isotropic exchange is also considered.  相似文献   

12.
The influence of an intense radiation fieldE0 on the magnon damping in free carrier magnetic semiconductors is discussed. It is shown that the effect of the intense field is to give a drift velocity v0 = eE0/mΩ to the carriers such that when v0 exceeds the phase velocity of the spin waves the electrons are more able to emit magnons than they absorb and as a consequence the magnon population grows with time.  相似文献   

13.
An action-angle representation of spin variables is used to relate the large-S Heisenberg antiferromagnet to the O(3) nonlinear sigma model quantum field theory, with precise equivalence for integral S. A variant theory is found for half-integral S. Dynamic mass generation by the Néel magnon is predicted.  相似文献   

14.
成泰民  罗宏超  李林 《物理学报》2008,57(10):6531-6539
在二维复式正方Heisenberg铁磁系统的基础上建立了磁振子-声子相互作用模型.利用松原格林函数理论研究了系统的磁振子寿命,计算了布里渊区的主要对称点线上的磁振子衰减的变化曲线,比较了磁性离子的与非磁性离子的光频支声子对磁振子衰减的影响以及各项参数的变化和温度对磁振子衰减的影响.发现光频支声子-磁振子耦合对磁振子衰减起主要作用,尤其是纵向光频支声子对磁振子衰减起更大的作用,并且非磁性离子的光频支声子对磁振子衰减的作用比磁性离子的光频支声子对磁振子衰减的作用更显著.根据关系式-Im*(1)(k)=/(2τ)可以对磁振子寿命进行判断. 关键词: 光频支声子-磁振子相互作用 磁振子衰减 磁振子寿命 绝缘复式正方铁磁体系统  相似文献   

15.
Thermoelectric power in antiferromagnetic semiconductors is calculated in the vicinity of the Néel temperature by assuming the presence of the well-defined propagating modes (magnon) and a temperature-dependent magnon velocity. Carriers are specified by the mobile carriers in a broad band with an isotropic effective mass. Magnons and carriers are coupled via the sd-interaction. Anomaly near TN does not result from the diffusion term Sdiff. and it is ascribed to the magnon-drag contribution Sdrag which is obtained from
Sdrag=?qR(q)cm(q)/3e
,where R(q) is the momentum transfer ratio between the magnon system and carriers, cm(q) denotesthe specific heat of the magnon q. The assumed temperature dependence of the magnon velocity makesSdru divergent at TN with TN ? T → +0 and it might be removed in consideration of the magnon frequency spreading. Except this divergence the calculation provides a qualitative explanation for the anomalous feature in MnTe.  相似文献   

16.
Within the Hubbard model, two boson Green’s functions that describe the propagation of collective excitations of the electronic system—magnons (states with a single electron spin flip) and doublons (states with two electrons at one site of the crystal lattice)—are calculated for a Coulomb interaction of arbitrary strength and for an arbitrary electron concentration by applying a decoupling procedure to the double-time X-operator Green’s functions. It is found that the magnon and doublon Green’s functions are similar in structure and there is a close analogy between them. Instability of the paramagnetic phase with respect to spin ordering is investigated using the magnon Green’s function, and instability of the metallic phase to charge ordering is analyzed with the help of the doublon Green’s function. Criteria for the paramagnet-ferromagnet and metal-insulator phase transitions are found.  相似文献   

17.
低温下二维绝缘铁磁体的磁振子寿命   总被引:3,自引:0,他引:3       下载免费PDF全文
成泰民  鲜于泽  杜安 《物理学报》2005,54(11):5314-5323
在二维正方绝缘铁磁系统基础上建立了一个磁振子-声子相互作用模型. 利用格林函数方法研究了磁振子-声子相互作用下的二维绝缘铁磁体的磁振子衰减(即-ImΣ*(1)(k)), 计算了布里渊区的主要对称点线上的-ImΣ*(1)(k).发现在布里渊区边界区域磁振子衰减很明显, 但小波矢区(kxa/π<0.22附近)磁振子衰减非常弱, 而且温度很低时磁振子衰减有极大值. 比较了纵向声子与横向声子对磁振子衰减的影响, 也讨论了各项参数的变化对磁振子衰减的影响. 根据关系式-Im*(1)(k)=/(2τ)可以对磁振子寿命进行判断. 关键词: 磁振子-声子相互作用 磁振子衰减 铁磁体 磁振子寿命  相似文献   

18.
It is shown that the finite size corrections to the spectrum of the giant magnon solution of classical string theory, computed using the uniform light-cone gauge, are gauge invariant and have physical meaning. This is seen in two ways: from a general argument where the single magnon is made gauge invariant by putting it on an orbifold as a wrapped state obeying the level matching condition as well as all other constraints, and by an explicit calculation where it is shown that physical quantum numbers do not depend on the uniform light-cone gauge parameter. The resulting finite size effects are exponentially small in the R-charge and the exponent (but not the prefactor) agrees with gauge theory computations using the integrable Hubbard model.  相似文献   

19.
Hybridized magnonic–photonic systems promise novel applications for future information processing technologies. Here, a hybrid magnonic system comprising of a qutrit (Λ-type three-level atom) and a ferromagnetic YIG sphere is considered. Indeed, the whole system is driven by two light fields under the influence of the thermal environment. The indirect magnon–atom interaction is established via the virtual photon exchange. The associated Lindblad master equation is derived and its solution is found to investigate the nonclassical feature, especially in the steady-state solution. Generally, the system shows considerable nonclassicality, that is, strong magnon antibunching and magnon blockade. In fact, the feasibility of using such a hybrid system to prepare a single-magnon source based on magnon blockade effects we theoretically demonstrated. Besides, the considered system may be exploited to generate robust and stable magnon–atom entanglement. The appearance of magnon blockade and magnon–atom entanglement in the Λ-type atom may have its origin in the fact that the atom is trapped in different superposition states, induced by the quantum interference phenomenon. The proposed model and the corresponding results may open up an intriguing prospect to prepare a single-magnon source and provide further benefits through concatenating with photons in optomagnonic systems.  相似文献   

20.
We present the perturbation theory for lattice magnon fields of the DD-dimensional O(3) Heisenberg ferromagnet. The effective Hamiltonian for the lattice magnon fields is obtained starting from the effective Lagrangian, with two dominant contributions that describe magnon–magnon interactions identified as a usual gradient term for the unit vector field and a part originating in the Wess–Zumino–Witten term of the effective Lagrangian. Feynman diagrams for lattice scalar fields with derivative couplings are introduced, on the basis of which we investigate the influence of magnon–magnon interactions on magnon self-energy and ferromagnet free energy. We also comment appearance of spurious terms in low-temperature series for the free energy by examining magnon–magnon interactions and internal symmetry of the effective Hamiltonian (Lagrangian).  相似文献   

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