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 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.
A mobile spin-triplet excitation above a singlet background in a quantum magnet. At low density, an appropriate triplet branch can be described as bosonic quasiparticles with an effective mass and repulsive interaction. Applied magnetic field can lower one branch toward condensation. The term does not imply that the total excitation number is conserved on thermodynamic timescales.
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A magnon is a quasi-particle used to describe collective excitations of the magnetic order in a material. In condensed matter physics, magnons arise in the context of magnetic systems, particularly in ferromagnets and antiferromagnets. They represent quantized spin waves, which are disturbances in the arrangement of spins (magnetic moments) of electrons in a solid.