magnons
Magnons are defined as collective excitations of a magnetic lattice that possesses long range magnetic order; more specifically, a single
magnon excitation corresponds to the change by one unit of the magnetic moment of the lattice or system. This non-local nature of magnons is the cause of the experimentally observed dispersive behavior, that is a non-linear or non-constant relation
between the transferred momentum
and the transferred energy of the magnetic lattice upon its excitation. Typical values for the peak(s) of the transferred energy are on the order of 0.5 eV to 2 eV.
Two- and mutiple- magnon dispersion
phenomena have been reported, and were recently employed to explain the nonlinear dispersion behavior of both crystalline and non-crystalline systems with long range ordering compared with the atomic scale.
Experimentally, magnon dispersions have been detected by resonant microwave
absorption
in external magnetic fields
(that is, by Spin-Wave resonance
excitation (SWR) and ferromagnetic resonance (FMR)) for ferromagnetic metallic glasses
at ambient temperatures. Several neutron
inelastic, as well as Cu
edge resonant inelastic X-ray
scattering (RIXS), spectra were also reported for crystaline materials such as the undoped antiferromagnetic cuprates below 20 K.
Such measurements and corresponding theories are of significant interest for an improved understanding of high temperature superconductivity; upon doping ( for example with Ytrium or Lanthanum, and Barium) the long-range ordering in a antiferromagnetic lattice- that was present in certain undoped copper oxide insulators- becomes frustrated, thus leading to short range antiferromagnetic fluctuations, symmetry breaking and high temperature superconductivity.
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