On a ferromagnetic spin chain

The quotient (s-1)/(s) of Riemann zeta functions is shown to be the partition function of a ferromagnetic spin chain for inverse temperatures.     

Solitons on a discrete ferromagnetic spin chain

Discrete ferromagnetic spin chains with planar single-ion and exchange anisotropy and with an externaldc fieldB applied in the easy plane are considered in the classical limit. We find two different static in-plane kink structures, which are symmetric with respect to a given spin or to a given bond of the chain, respectively. The first structure is unstable against in-plane fluctuations for all applied fields. The second one, on the other hand, exists (independent of the anisotropy parameters) only up to a critical fieldB _e and is stable against in-plane fluctuations in its whole domain of existence. Depending on the anisotropy parameters, this latter configuration may, however, become unstable against out-of-plane fluctuations at a critical valueB _c <B _e of the external field. Both types of kink structures can also move along the chain, by developing an out-of-plane spin component. With increasing velocity, the kink motion leads to a rapid reduction of the critical field marking the existence limit of these spin structures. The discreteness is found to have substantial influence on the spectrum of the solitons.Work supported by the Bundesministerium für Forschung und TechnologieWork supported by Schweizerischer Nationalfonds     

Thermoelectric spin diffusion in a ferromagnetic metal

We present a semiclassical theory of spin diffusion in a ferromagnetic metal subject to a temperature gradient. Spin-flip scattering can generate pure thermal spin currents by short-circuiting spin channels while suppressing spin accumulations. A thermally induced spin density is locally generated when the energy dependence of the density of states is spin polarized.     

sd-Exchange electron spin resonance in a ferromagnetic metal

The possibility of resonance absorption in the terahertz range caused by the sd-exchange interaction at the incidence of an electromagnetic wave on a ferromagnetic metal has been predicted. The absorption coefficient has been calculated. It has been shown that the resonance frequency is determined by the magnetization of a ferromagnet and the absorption coefficient additionally depends on the orientation of the magnetization with respect to the plane of polarization of the wave.     

The SYM integrable super spin chain

Recently it was established that the one-loop planar dilatation generator of super-Yang–Mills theory may be identified, in some restricted cases, with the Hamiltonians of various integrable quantum spin chains. In particular Minahan and Zarembo established that the restriction to scalar operators leads to an integrable vector chain, while recent work in QCD suggested that restricting to twist operators, containing mostly covariant derivatives, yields certain integrable Heisenberg XXX chains with non-compact spin symmetry . Here we unify and generalize these insights and argue that the complete one-loop planar dilatation generator of is described by an integrable super spin chain. We also write down various forms of the associated Bethe ansatz equations, whose solutions are in one-to-one correspondence with the complete set of all one-loop planar anomalous dimensions in the gauge theory. We finally speculate on the non-perturbative extension of these integrable structures, which appears to involve non-local deformations of the conserved charges.     

The dynamics of a generalized Heisenberg ferromagnetic spin chain

We introduce a generalized Heisenberg ferromagnetic spin chain with a four-dimensional target space, and investigate its continuous limit, the generalized continuous Heisenberg model (GCHM). We reduce the dynamics of the GCHM to a nonlinear evolution of space curves in four dimensions. The space curve evolution is expressed in terms of a system of coupled nonlinear equations for the three curvatures, k(1)(x),k(2)(x),k(3)(x), of a curve in R(4). Applying the Painleve analysis to the stationary equations, we conclude that GCHM, in general, is not integrable, unless k(1) is constant. We obtain explicit solutions of the resulting stationary system under the latter condition. (c) 1995 American Institute of Physics.     

Intrinsic localized modes of a classical discrete anisotropic Heisenberg ferromagnetic spin chain

We report several exact intrinsic localized mode solutions of the classical spin evolution equation of a one-dimensional anisotropic Heisenberg ferromagnetic spin chain in terms of Jacobian elliptic functions. These include one, two and three spin excitations. All these solutions have smooth anticontinuum limits. Their linear stability and semiclassical quantization are also discussed briefly.     

Dynamic and static excitations of a classical discrete anisotropic Heisenberg ferromagnetic spin chain

Using Jacobi elliptic function addition formulas and summation identities we obtain several static and moving periodic soliton solutions of a classical anisotropic, discrete Heisenberg spin chain with and without an external magnetic field. We predict the dispersion relations of these nonlinear excitations and contrast them with that of magnons and relate these findings to the materials realized by a discrete spin chain. As limiting cases, we discuss different forms of domain wall structures and their properties.     

Bright and dark solitons for a variable-coefficient $$$$ dimensional Heisenberg ferromagnetic spin chain equation

Under investigation in this paper is a variable-coefficient \((2+1)\) dimensional Heisenberg ferromagnetic spin chain equation. Bilinear forms for the bright and dark soliton solutions are respectively obtained. Bright and dark solitons are obtained via the Hirota bilinear method. Features of the bright and dark solitons are discussed. Interaction properties of the bright and dark solitons are discussed via the asymptotic analysis, and stability of the bright and dark solitons is studied via the numerical calculation: (1) Amplitudes of the bright and dark solitons are not related to the coefficient \(\delta _{4}(t)\), while the soliton velocities are related to \(\delta _{4}(t)\). (2) Interactions between the bright two solitons are shown to be elastic, while interactions between the dark two solitons could be elastic or inelastic, which is determined by the values of \(\rho \). (3) Numerical calculation indicates that the bright solitons could not resist the disturbance of small perturbations, while the dark solitons could resist the disturbance of small perturbations.     

Spin-independent transparency of pure spin current at normal/ferromagnetic metal interface

The spin transparency at the normal/ferromagnetic metal(NM/FM) interface was studied in Pt/YIG/Cu/FM multilayers. The spin current generated by the spin Hall effect(SHE) in Pt flows into Cu/FM due to magnetic insulator YIG blocking charge current and transmitting spin current via the magnon current. Therefore, the nonlocal voltage induced by an inverse spin Hall effect(ISHE) in FM can be detected. With the magnetization of FM parallel or antiparallel to the spin polarization of pure spin currents(σ(sc)), the spin-independent nonlocal voltage is induced. This indicates that the spin transparency at the Cu/FM interface is spin-independent, which demonstrates that the influence of spin-dependent electrochemical potential due to spin accumulation on the interfacial spin transparency is negligible. Furthermore, a larger spin Hall angle of Fe_(20)Ni_(80) (Py) than that of Ni is obtained from the nonlocal voltage measurements.     

The spin wave stiffness constant in itinerant electron ferromagnetic transition metal dilute alloys

The spin wave stiffness constant is calculated for itenerant electron ferromagnetic transition metal dilute alloys. Calculations are made in the Random Phase Approximation, using the method of effective magnon Hamiltonian. The term in the magnon energy proportional to impurity concentration is calculated by summing up exactly a perturbational series.     

一维铁磁/有机系统的基态与自旋分布研究

文中用一维紧束缚模型描述铁磁金属,用一维非简并的Su-Schrieffer -Heeger (SSH)模型描述共轭聚合物,研究了在一维铁磁/共轭聚合物系统和一维CMR材料/ 聚合物系统中的电子转移和自旋转移.发现在聚合物部分没有自旋的双极化子比有自旋的极化子具有较低的能量而容易产生.然而在铁磁CMR材料/聚合物系统中极化子的产生能低于聚合物中极化子的产生能,增加了有机物中自旋极化输运的可能性.     

Dipole-exchange spin excitations in a thin ferromagnetic nanoshell

In this paper spin excitations in spherical ferromagnetic nanoshells are investigated. The magnetic dipoledipole interaction, the exchange interaction and the anisotropy effects are taken into consideration. For such spin excitations, an equation for the magnetic potential perturbation is obtained. For a nanoshell that is thin compared to its size, the dispersion relation for nonzero spin excitation modes and the only possible frequency for zero-mode spin excitations are found. Limitations on the mode numbers are derived.     

Positive muon as a probe of magnetization density in ferromagnetic metal vacancies

The hyperfine field at a positive muon site trapped in a ferromagnetic metal vacancy is calculated and found to be more positive than that in the interstitial position. It is suggested that the muons can be used to enrich our knowledge of the electron spin distributions in metal vacancies that so far has not been possible.     

Fingerprints of the magnetic polaron in nonequilibrium electron transport through a quantum wire coupled to a ferromagnetic spin chain

We study nonequilibrium quantum transport through a mesoscopic wire coupled via local exchange to a ferromagnetic spin chain. Using the Keldysh formalism in the self-consistent Born approximation, we identify fingerprints of the magnetic polaron state formed by hybridization of electronic and magnon states. Because of its low decoherence rate, we find coherent transport signals. Both elastic and inelastic peaks of the differential conductance are discussed as a function of external magnetic fields, the polarization of the leads, and the electronic level spacing of the wire.     

The origin of spin current in YIG/nonmagnetic metal multilayers at ferromagnetic resonance

Spin pumping in yttrium-iron-garnet(YIG)/nonmagnetic-metal(NM) layer systems under ferromagnetic resonance(FMR) conditions is a popular method of generating spin current in the NM layer.A good understanding of the spin current source is essential in extracting spin Hall angle of the NM and in potential spintronics applications.It is widely believed that spin current is pumped from precessing YIG magnetization into NM layer.Here,by combining microwave absorption and DC-voltage measurements on thin YIG/Pt and YIG/NM_1/NM_2(NM_1 =Cu or Al,NM_2 =Pt or Ta),we unambiguously showed that spin current in NM,instead of from the precessing YIG magnetization,came from the magnetized NM surface(in contact with thin YIG),either due to the magnetic proximity effect(MPE) or from the inevitable diffused Fe ions from YIG to NM.This conclusion is reached through analyzing the FMR microwave absorption peaks with the DC-voltage peak from the inverse spin Hall effect(ISHE).The voltage signal is attributed to the magnetized NM surface,hardly observed in the conventional FMR experiments,and was greatly amplified when the electrical detection circuit was switched on.     

Chiral symmetry breaking in QCD; Mesons as spin waves

The strong chiral symmetry breaking in Wilson's lattice version of QCD is discussed and interpreted as a necessary manifestation of the triangle anomaly. At strong coupling the effective hamiltonian acting in the s-wave hadron sector is found to describe a generalized antiferromagnet which is analyzed with the $\text{1}\text{2}\text{S}\text{(= 1/N, N = N}{}_{\mathrm{<mtext>color</mtext>}}\text{)}$ expansion known in the theory of magnetism. Mesons emerge as spin waves: pseudoscalars as Nambu-Goldstone bosons, vectors as “dormant” Goldstone bosons. Current and dynamical quark masses are identified, such that m_P² ∫ m(cur), m_v≈2[m(cur) + m(fyn)], and a fit to the particle spectrum gives m(dyn) = 390 MeV, m_u,d(cur) = 5.4 MeV, m_s(cur) = 140 MeV, m_c(cur) = 1.07 GeV. Static baryons emerge with a mass m_B = N[m(dyn) + m(cur)] + a contribution which is argued to vanish in the continuum limit. Vector and axial vector currents are defined on the lattice and studied at strong coupling. The relations $\text{1 =}\text{3}\text{5}\text{g}{}_{\mathrm{<mtext>A</mtext>}}\text{γ}{}_{\mathrm{?}}\text{(f}{}_{\mathrm{\pi }}\text{/m}{}_{\mathrm{?}}\text{)(Z}{}_{\mathrm{\pi }}\text{/Z}{}_{\mathrm{?}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, Z_π/Z_? = 3.0 are found to agree with experiment. The resolution of the U(1) problem at strong coupling is discussed.     

Superconducting decay length in a ferromagnetic metal

The complex decay length ξ characterizing the penetration of superconducting correlations into a ferromagnet due to the proximity effect is studied theoretically in the framework of the linearized Eilenberger equations. The real part ξ₁ and imaginary part ξ₂ of the decay length are calculated as functions of exchange energy and the rates of ordinary, spin-flip, and spin-orbit electronic scattering in a ferromagnet. The lengths ξ_1,2 determine the spatial scales of, respectively, the decay and oscillation of a critical current in SFS Josephson junctions in the limit of a large distance between superconducting electrodes. The developed theory provides the criteria of applicability of the expressions for ξ₁ and ξ₂ in the dirty and clean limits, which are commonly used in the analysis of SF hybrid structures. The text was submitted by the authors in English.