77 research outputs found
Role of dimensionality in spontaneous magnon decay: easy-plane ferromagnet
We calculate magnon lifetime in an easy-plane ferromagnet on a tetragonal
lattice in transverse magnetic field. At zero temperature magnons are unstable
with respect to spontaneous decay into two other magnons. Varying ratio of
intrachain to interchain exchanges in this model we consider the effect of
dimensionality on spontaneous magnon decay. The strongest magnon damping is
found in the quasi-one-dimensional case for momenta near the Brillouin zone
boundary. The sign of a weak interchain coupling has a little effect on the
magnon decay rate. The obtained theoretical results suggest possibility of
experimental observation of spontaneous magnon decay in a quasi-one-dimensional
ferromagnet CsNiF. We also find an interesting enhancement of the magnon
decay rate for a three-dimensional ferromagnet. The effect is present only for
the nearest-neighbor model and is related to effective dimensionality reduction
in the two-magnon continuum.Comment: 6 pages, 6 figure
Spontaneous magnon decays in planar ferromagnet
We predict that spin-waves in an easy-plane ferromagnet have a finite
lifetime at zero temperature due to spontaneous decays. In zero field the
damping is determined by three-magnon decay processes, whereas decays in the
two-particle channel dominate in a transverse magnetic field. Explicit
calculations of the magnon damping are performed in the framework of the
spin-wave theory for the square-lattice ferromagnet with an anisotropy
parameter . In zero magnetic field the decays occur for
with . We also discuss possibility
of experimental observation of the predicted effect in a number of
ferromagnetic insulators.Comment: 6 pages, 6 figures, to appear in Europhysics Letter
The enhancement of ferromagnetism in uniaxially stressed diluted magnetic semiconductors
We predict a new mechanism of enhancement of ferromagnetic phase transition
temperature in uniaxially stressed diluted magnetic semiconductors (DMS)
of p-type. Our prediction is based on comparative studies of both Heisenberg
(inherent to undistorted DMS with cubic lattice) and Ising (which can be
applied to strongly enough stressed DMS) models in a random field approximation
permitting to take into account the spatial inhomogeneity of spin-spin
interaction. Our calculations of phase diagrams show that area of parameters
for existence of DMS-ferromagnetism in Ising model is much larger than that in
Heisenberg model.Comment: Accepted for publication in Phys. Rev.
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