共查询到20条相似文献,搜索用时 31 毫秒
1.
Yu.A. Fridman O.A. Kosmachev D.A. Matunin G.A. Gorelikov Ph.N. Klevets 《Journal of magnetism and magnetic materials》2010,322(20):3196-3203
We investigated the influence of strong single-ion anisotropy, exceeding exchange interaction, and frustrated exchange interaction on spin-wave excitation spectra and phase states using the Hubbard operators’ technique, allowing the exact account of single-ion anisotropy. The results show that both the homogeneous phases (ferromagnetic and quadrupolar) and the spatially inhomogeneous phase (spiral structure) are possible in the 3D magnetic crystal. The region of existence of the spiral structure is considerably smaller than that in the analogues system, but with weak single-ion anisotropy. The situation is more complex in the 2D system; another spatially inhomogeneous state (the domain structure) can be realized in addition to the spiral magnetic structure. The phase diagrams for both the 3D and 2D systems were plotted. 相似文献
2.
I. V. Bychkov D. A. Kuzmin V. G. Sharov 《Bulletin of the Russian Academy of Sciences: Physics》2013,77(3):278-280
The spectrum of coupled spin, elastic, and electromagnetic waves in the magnetic of a ferromagnetic spiral phase is investigated. The frequency dependences of the reflection coefficient of electromagnetic waves from the surface of a semi-infinite magnet for different angles of the spiral are obtained. An acoustic analog of the Faraday effect in the magnetics of a ferromagnetic spiral phase is considered. 相似文献
3.
Interaction of spiral waves in a two-layer system described by a model of coupled complex Ginzburg-Landau equations with negative-feedback couplings ε(1) and ε(2) is studied. Synchronization of two spiral waves can be broadly found if ε(1)+ε(2) is sufficiently large. Prior to the synchronization, under the condition of strongly asymmetric coupling (∣ε(1)-ε(2)∣?0), a novel type of spiral wave, amplitude spiral wave, exists in the driven system. The pattern of amplitude spiral wave shows the spiral in the amplitude and without a singularity point (tip), compared to usual spiral waves known for phase with amplitude uniform far away from tips and rotating around tips. 相似文献
4.
The bond-alternative ferromagnetic Ising model with the Dzyaloshinskii-Moriya (DM) interaction is investigated using an infinite time-evolving block decimation (iTEBD) algorithm, and two interesting phase diagrams are proposed. Without bond alternation, there are only two well-known phases (a ferromagnetic phase and an x-y spiral (chiral Luttinger liquid) phase). Once the bond alternation is taken into account, two additional interesting phases (a z-chiral and a z-stripe phases) are induced. Nonzero chiral order is observed in all phases except the ferromagnetic phase. Two kinds of chiral phase, with or without string order, are identified. With the y-axis DM interaction, the phase diagram becomes relatively simple, and consists of only two different phases (a ferromagnetic phase and a y-chiral phase). First-order metamagnetic phase transitions from the ferromagnetic phase into the other phases are observed in both cases. 相似文献
5.
Y. Liu J. Dong D.Y. Xing 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):185-188
Minimizing total free energy by numerical calculations, we obtain the magnetic phase diagram of perovskite Mn oxides, such
as with , Ca, Sr, etc. in the whole doping region from x
=0 to x
=1 at temperature T
=0. It is discovered that a spiral state is stable in a low concentration of X ions while a canted state is stable in a high
concentration of X ions, and a ferromagnetic phase can exist in the intermediate concentrations when the antiferromagnetic
interaction is weak. The energy difference between spiral and canted states is found to be small when the Hund coupling is
large. Magnetic field induced spiral/canted phase transition is considered as a possible mechanism of the colossal magnetoresistance
(CMR) in the Mn oxides.
Received: 11 July 1996 / Revised: 7 December 1996 / Accepted: 24 July 1997 相似文献
6.
We calculate the spectrum of collective excitations of the XY spiral state prepared adiabatically or suddenly from a uniform ferromagnetic F=1 condensate. For spiral wave vectors past a critical value, spin wave excitation energies become imaginary indicating a dynamical instability. We construct phase diagrams as functions of spiral wave vector and quadratic Zeeman energy. 相似文献
7.
Measurements of the elastic constant c33 for Tb-50% Ho, as a function of temperature and magnetic field, have been used to determine the magnetic phase diagram of the alloy. Evidence for the four phases:paramagnetic, spiral spin antiferromagnetic, fan and ferromagnetic are presented. The true ferromagnetic phase is only found below 100 K even in fields of up to 7 Tesla. 相似文献
8.
9.
Effects of temperature on magnetic phase separation and on the parameters of spin-spiral waves are studied. The study is performed
using the two-dimensional single-band Hubbard model and the Hubbard-Stratonovich transformation. Both commensurate (antiferromagnetic,
ferromagnetic) and incommensurate (spiral) magnetic phases are considered. The problem is solved using the static approximation
with allowance for transverse fluctuations of the magnetic moment. It is shown that the temperature significantly affects
the collinear and spiral magnetic phases. With an increase in the temperature, the phase-separation region near the half-filling
is sufficiently reduced and substituted by the antiferromagnetic phase. The results are used for the interpretation of the
magnetic properties of cuprates. 相似文献
10.
Yu. A. Fridman D. A. Matyunin F. N. Klevets G. A. Gorelikov 《Physics of the Solid State》2010,52(6):1196-1203
The possibility of forming a modulated (spiral) magnetic structure in anisotropic Heisenberg and non-Heisenberg magnets with
a frustrated Heisenberg exchange interaction has been investigated. It has been demonstrated that, apart from homogeneous
(ferromagnetic and quadrupole) states, the Heisenberg magnets with a strong easy-plane anisotropy can have a spiral magnetic
structure. The axis of the spiral coincides with the direction of the external magnetic field. The inclusion of the biquadratic
exchange interaction leads to a narrowing of the magnetic field region of the existence of the spiral structure. In the absence
of the external magnetic field, the spiral structure can be formed only in the case of easy-axis anisotropy. 相似文献
11.
Temperature-induced phase transitions in a uniaxial ferromagnetic system of spins S = 1 with competing one-particle and two-particle anisotropies are studied. It is shown that, in the case where easy-plane single-ion anisotropy dominates over easy-axis two-particle anisotropy, the transition from the paramagnetic state to a ferromagnetic state with magnetization perpendicular to the anisotropy axis is a second-order displacive magnetic phase transition. In the opposite case, where two-particle anisotropy dominates over single-particle anisotropy, the transition to a ferromagnetic state with magnetization perpendicular to the anisotropy axis is also continuous but of the order-disorder type. In a system with competing second-order one-and two-particle anisotropies, the orientational first-order phase transition can occur to a state with the magnetization directed along or perpendicular to the anisotropy axis. 相似文献
12.
Stochastic resonance and nonequilibrium dynamic phase transition of Ising spin system driven by a joint external field 下载免费PDF全文
The dynamic response and stochastic resonance of a kinetic Ising spin system (ISS) subject to the joint action of an external field of weak sinusoidal modulation and stochastic white-nolse are studied by solving the mean-field equation of motion based on Glauber dynamics. The periodically driven stochastic ISS shows that the characteristic stochastic resonance as well as nonequilibrium dynamic phase transition (NDPT) occurs when the frequency ω and amplitude h0 of driving field, the temperature t of the system and noise intensity D are all specifically in accordance with each other in quantity. There exist in the system two typical dynamic phases, referred to as dynamic disordered paramagnetic and ordered ferromagnetic phases respectively, corresponding to a zero- and a unit-dynamic order parameter. The NDPT boundary surface of the system which separates the dynamic paramagnetic phase from the dynamic ferromagnetic phase in the 3D parameter space of ho-t-D is also investigated. An interesting dynamical ferromagnetic phase with an intermediate order parameter of 0.66 is revealed for the first time in the ISS subject to the perturbation of a joint determinant and stochastic field. The intermediate order dynamical ferromagnetic phase is dynamically metastable in nature and owns a peculiar characteristic in its stability as well as the response to external driving field as compared with a fully order dynamic ferromagnetic phase. 相似文献
13.
Ferriani P von Bergmann K Vedmedenko EY Heinze S Bode M Heide M Bihlmayer G Blügel S Wiesendanger R 《Physical review letters》2008,101(2):027201
Using spin-polarized scanning tunneling microscopy we show that the magnetic order of 1 monolayer Mn on W(001) is a spin spiral propagating along 110 crystallographic directions. The spiral arises on the atomic scale with a period of about 2.2 nm, equivalent to only 10 atomic rows. Ab initio calculations identify the spin spiral as a left-handed cycloid stabilized by the Dzyaloshinskii-Moriya interaction, imposed by spin-orbit coupling, in the presence of softened ferromagnetic exchange coupling. Monte Carlo simulations explain the formation of a nanoscale labyrinth pattern, originating from the coexistence of the two possible rotational domains, that is intrinsic to the system. 相似文献
14.
The nonlinear dynamics of a periodic system of interacting domain walls in a thin ferromagnetic uniaxial film with transverse
anisotropy is examined. The interaction between the domain walls takes place through the magnetostatic demagnifying fields
of the domains. The equations of motion derived for such a system of walls are solved numerically by a 4–5th-order Runge-Kutta
scheme, while the uniformity of the distributions of the phase trajectory, the form of the Poincaré cross section, and the
spectral density of the vibrations serve as indicators of the type of oscillations. All the known types of oscillations are
observed in a computer simulation of this nonlinear system: periodic, quasiperiodic, and chaotic. The computational results
have a universal character for uniaxial, highly-anisotropic ferromagnetic films having a strip domain structure, since the
results can be easily scaled for materials with different magnetic characteristics.
Fiz. Tverd. Tela (St. Petersburg) 39, 2036–2039 (November 1997) 相似文献
15.
Phase diagrams in mixed spin-3/2 and spin-2 Ising system with two alternative layers within the effective-field theory 下载免费PDF全文
The phase diagrams in the mixed spin-3/2 and spin-2 Ising system with two alternative layers on a honeycomb lattice are investigated and discussed by the use of the effective-field theory with correlations. The interaction of the nearest-neighbour spins of each layer is taken to be positive (ferromagnetic interaction) and the interaction of the adjacent spins of the nearest-neighbour layers is considered to be either positive or negative (ferromagnetic or anti-ferromagnetic interaction). The temperature dependence of the layer magnetizations of the system is examined to characterize the nature (continuous or discontinuous) of the phase transitions and obtain the phase transition temperatures. The system exhibits both second-and first-order phase transitions besides triple point (T P ), critical end point (E), multicritical point (A), isolated critical point (C) and reentrant behaviour depending on the interaction parameters. We have also studied the temperature dependence of the total magnetization to find the compensation points, as well as to determine the type of behaviour, and N-type behaviour in N′eel classification nomenclature existing in the system. The phase diagrams are constructed in eight different planes and it is found that the system also presents the compensation phenomena depending on the sign of the bilinear exchange interactions. 相似文献
16.
I. V. Bychkov D. A. Kuz’min V. V. Shadrin V. G. Shavrov 《Bulletin of the Russian Academy of Sciences: Physics》2012,76(3):368-370
The spectrum of coupled spin and electromagnetic waves is obtained for a magnetic with a ferromagnetic spiral structure determined
by nonuniform exchange and relativistic interactions. It is shown that resonant interaction between spin and electromagnetic
waves is possible. The electromagnetic wave reflectance from the plate of a magnetic with a ferromagnetic spiral is calculated
for different spiral angles. 相似文献
17.
采用Hindmarsh-Rose(HR)神经元模型,研究了二维神经元阵列系统从一个具有随机相位分布的初态演化最终是否能自发产生螺旋波的问题.数值结果表明:系统是否出现螺旋波与单个HR神经元的状态、系统的初态和耦合强度有关,其中单个HR神经元的振荡状态起主要作用.当单个HR神经元处于一周期振荡态时,在一定的耦合强度范围内系统都会自发出现多个螺旋波和螺旋波对,出现螺旋波与系统初态无关,只要适当选择耦合强度,在系统中可以出现单个螺旋波.当耦合强度超过某一阈值后,继续增加耦合强度,系统会呈现三种不同的动力学行为,分别与三类初态有关.系统从第一类初态演化将偶尔出现单个螺旋波,系统从第二类和第三类初态演化将分别出现间歇性全局同步振荡和振荡死亡.当单个神经元处于二周期态时,只有当系统神经元的初相位比较均匀分布时,系统才能自发出现螺旋波,而且出现螺旋波的耦合强度范围大为减少.当神经元处于更高的周期态时,系统一般不容易自发出现螺旋波.这些结果有助于人们了解大脑皮层自发产生螺旋波的机制. 相似文献
18.
The electrical coupling of myocytes and fibroblasts can play a role in inhibiting electrical impluse propagation in cardiac muscle. To understand the function of fibroblast–myocyte coupling in the aging heart, the spiral-wave dynamics in the duplex networks with inhibitory coupling is numerically investigated by the Br–Eiswirth model. The numerical results show that the inhibitory coupling can change the wave amplitude, excited phase duration and excitability of the system. When the related parameters are properly chosen, the inhibitory coupling can induce local abnormal oscillation in the system and the Eckhaus instability of the spiral wave. For the dense inhibitory network, the maximal decrement(maximal increment) in the excited phase duration can reach 24.3%(13.4%), whereas the maximal decrement in wave amplitude approaches 28.1%. Upon increasing the inhibitory coupling strength, the system excitability is reduced and even completely suppressed when the interval between grid points in the inhibitory network is small enough. Moreover, the inhibitory coupling can lead to richer phase transition scenarios of the system, such as the transition from a stable spiral wave to turbulence and the transition from a meandering spiral wave to a planar wave. In addition, the self-sustaining planar wave, the unique meandering of spiral wave and inward spiral wave are observed. The physical mechanisms behind the phenomena are analyzed. 相似文献
19.
20.
White JS Honda T Kimura K Kimura T Niedermayer Ch Zaharko O Poole A Roessli B Kenzelmann M 《Physical review letters》2012,108(7):077204
The olivine compound Mn(2)GeO(4) is shown to feature both a ferroelectric polarization and a ferromagnetic magnetization that are directly coupled and point along the same direction. We show that a spin spiral generates ferroelectricity, and a canted commensurate order leads to weak ferromagnetism. Symmetry suggests that the direct coupling between the ferromagnetism and ferroelectricity is mediated by Dzyaloshinskii-Moriya interactions that exist only in the ferroelectric phase, controlling both the sense of the spiral rotation and the canting of the commensurate structure. Our study demonstrates how multicomponent magnetic structures found in magnetically frustrated materials like Mn(2)GeO(4) provide a new route towards functional materials that exhibit coupled ferromagnetism and ferroelectricity. 相似文献