Talk:PlanetPhysics/Magnons

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\section{Magnons and magnon dispersion}

{\em Magnons} are defined as collective excitations of a magnetic lattice that possesses long range magnetic order; more specifically, a single {\em magnon} excitation corresponds to the change by one unit of the magnetic moment of the lattice or \htmladdnormallink{system}{http://planetphysics.us/encyclopedia/SimilarityAndAnalogousSystemsDynamicAdjointnessAndTopologicalEquivalence.html}. This non-local nature of magnons is the cause of the experimentally observed dispersive behavior, that is a non-linear or non-constant \htmladdnormallink{relation}{http://planetphysics.us/encyclopedia/Bijective.html} between the transferred \htmladdnormallink{momentum}{http://planetphysics.us/encyclopedia/Momentum.html} and the transferred \htmladdnormallink{energy}{http://planetphysics.us/encyclopedia/CosmologicalConstant.html} 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- \htmladdnormallink{magnon dispersion}{http://planetphysics.us/encyclopedia/LondonEquation.html} 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.

\subsection{Experimental observation of the non-linear magnon dispersion} Experimentally, magnon dispersions have been detected by resonant \htmladdnormallink{microwave}{http://planetphysics.us/encyclopedia/FluorescenceCrossCorrelationSpectroscopy.html} \htmladdnormallink{absorption}{http://planetphysics.us/encyclopedia/FluorescenceCrossCorrelationSpectroscopy.html} in external \htmladdnormallink{magnetic fields}{http://planetphysics.us/encyclopedia/NeutrinoRestMass.html} (that is, by Spin-Wave \htmladdnormallink{resonance}{http://planetphysics.us/encyclopedia/QualityFactorOfAResonantCircuit.html} excitation (SWR) and ferromagnetic resonance (FMR)) for ferromagnetic \htmladdnormallink{metallic glasses}{http://planetphysics.us/encyclopedia/LongRangeCoupling.html} at ambient \htmladdnormallink{temperatures}{http://planetphysics.us/encyclopedia/BoltzmannConstant.html}. Several \htmladdnormallink{neutron}{http://planetphysics.us/encyclopedia/Pions.html} inelastic, as well as Cu $K_\alpha$ edge resonant inelastic \htmladdnormallink{X-ray}{http://planetphysics.us/encyclopedia/FluorescenceCrossCorrelationSpectroscopy.html} scattering (RIXS), spectra were also reported for crystaline materials such as the undoped antiferromagnetic cuprates below 20 K.

\subsection{Applications} Such measurements and corresponding theories are of significant interest for an improved understanding of high temperature \htmladdnormallink{superconductivity}{http://planetphysics.us/encyclopedia/LongRangeCoupling.html}; 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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