893 research outputs found
Propagation of solitons of the magnetization in magnetic nano-particle arrays
It is clarified for the first time that solitons originating from the dipolar
interaction in ferromagnetic nano-particle arrays are stably created. The
characteristics can be well controlled by the strength of the dipolar
interaction between particles and the shape anisotropy of the particle. The
soliton can propagate from a particle to a neighbor particle at a clock
frequency even faster than 100 GHz using materials with a large magnetization.
Such arrays of nano-particles might be feasible in an application as a signal
transmission line.Comment: RevTeX, 3 pages, 3 PostScript figures, To appear in Journal of
Magnetism and Magnetic Material
Cluster expansion for dimerized spin systems
We have studied dimerized spin systems by realizing the cluster expansion to
high order. We have extended our previous dimer expansion for one-dimensional
systems to cover weakly interacting chains for a quantitative description of
three dimensional materials like PHCC and KCuCl_3. By comparison with recent
inelastic neutron scattering data we are able to determine the exchange
energies between individual spins. We have further investigated the
incommensurate region of zigzag chains with isotropic exchange coupling
constants near the disorder-line where the dispersion curve exhibits a minimum
at a finite wavevector. Our approach clearly shows the gradual transition
between the minimum of the dispersion at wavevector 0 and wavevector Pi within
this region. The extent of the incommensurate regime is given analytically in
an expansion in the coupling constants.Comment: 3 pages, 3 figures; contribution to ICNS2001; uses svjour.clo,
svglobal.clo (included
Dynamics of the Distorted Diamond Chain
We present results on the dynamics of the distorted diamond chain, S=1/2
dimers alternating with single spins 1/2 and exchange couplings and
in between. The dynamics in the spin fluid (SF) and tetramer-dimer (TD) phases
is investigated numerically by exact diagonalisation for up to 24 spins.
Representative excitation spectra are presented, both for zero magnetic field
and in the 1/3 plateau phase and the relevant parameters are determined across
the phase diagram. The behavior across the SF-TD phase transition line is
discussed for the specific heat and for excitation spectra. The relevance of
the distorted diamond chain model for the material Cu(CO)(OH)
(azurite) is discussed with particular emphasis on inelastic neutron scattering
experiments, a recent suggestion of one possibly ferromagnetic coupling
constant is not confirmed.Comment: 24 pages, 8 figure
Response functions of gapped spin systems in high magnetic field
We study the dynamical structure factor of gapped one-dimensional spin
systems in the critical phase in high magnetic field. It is shown that the
presence of a ``condensate'' in the ground state in the high-field phase leads
to interesting signatures in the response functions.Comment: uses ptptex.sty (included), 10 pages, 3 figs, to appear in Prog.
Theor. Phys. Suppl. (Proc. of the 16th Nishinomiya Yukawa Memorial Symposium
Nonlinear dynamics of the classical isotropic Heisenberg antiferromagnetic chain: the sigma model sector and the kink sector
We identify two distinct low-energy sectors in the classical isotropic
antiferromagnetic Heisenberg spin-S chain. In the continuum limit, we show that
two types of rotation generators arise for the field in each sector. Using
these, the Lagrangian for sector I is shown to be that of the nonlinear sigma
model. Sector II has a null Lagrangian; Its Hamiltonian density is just the
Pontryagin term. Exact solutions are found in the form of magnons and
precessing pulses in I and moving kinks in II. The kink has `spin' S. Sector I
has a higher minimum energy than II.Comment: 4 page
Ground-state phases of rung-alternated spin-1/2 Heisenberg ladder
The ground-state phase diagram of Heisenberg spin-1/2 system on a two-leg
ladder with rung alternation is studied by combining analytical approaches with
numerical simulations. For the case of ferromagnetic leg exchanges a unique
ferrimagnetic ground state emerges, whereas for the case of antiferromagnetic
leg exchanges several different ground states are stabilized depending on the
ratio between exchanges along legs and rungs. For the more general case of a
honeycomb-ladder model for the case of ferromagnetic leg exchanges besides
usual rung-singlet and saturated ferromagnetic states we obtain a ferrimagnetic
Luttinger liquid phase with both linear and quadratic low energy dispersions
and ground state magnetization continuously changing with system parameters.
For the case of antiferromagnetic exchanges along legs, different dimerized
states including states with additional topological order are suggested to be
realized
Finite Temperature Dynamics of the Spin 1/2 Bond Alternating Heisenberg Antiferromagnetic Chain
We present results for the dynamic structure factor of the S=1/2 bond
alternating Heisenberg chain over a large range of frequencies and
temperatures. Data are obtained from a numerical evaluation of thermal averages
based on the calculation of all eigenvalues and eigenfunctions for chains of up
to 20 spins. Interpretation is guided by the exact temperature dependence in
the noninteracting dimer limit which remains qualitatively valid up to an
interdimer exchange . The temperature induced central peak
around zero frequency is clearly identified and aspects of the crossover to
spin diffusion in its variation from low to high temperatures are discussed.
The one-magnon peak acquires an asymmetric shape with increasing temperature.
The two-magnon peak is dominated by the S=1 bound state which remains well
defined up to temperatures of the order of J. The variation with temperature
and wavevector of the integrated intensity for one and two magnon scattering
and of the central peak are discussed.Comment: 8 pages, 8 figure
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