Magnon (source code)
= Magnon
{wiki}
A magnon is one quantum of a <spin wave>, a collective oscillation of magnetic order. Exchange-coupled spins do not fluctuate independently: a disturbance spreads through the ordered system as a mode with a definite <wavevector> and <energy>.
In a simple collinear <Heisenberg ferromagnet>, a single magnon reduces the total spin projection along the ordered axis by one unit of $\hbar$ while distributing the disturbance across many sites. At low excitation density, magnon modes can be treated approximately as <bosonic> oscillators, motivating the <Holstein–Primakoff transformation> and <linear spin-wave approximation>. Their population contributes to the reduction of magnetization with increasing <temperature>. Strong interactions, noncollinear order and large excitation densities can require corrections to the simple independent-magnon picture.
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