by Nikuni et al. and in a ferrimagnet by Demokritov et al. at room temperature. In 2015 Uchida et al. reported the generation of spin currents by surface plasmon resonance. Paramagnons Paramagnons are magnons in magnetic materials which are in their high temperature, disordered (paramagnetic) phase. For low enough temperatures, the local atomic magnetic moments (spins) in ferromagnetic or anti-ferromagnetic compounds will become ordered. Small oscillations of the moments around their natural direction will propagate as waves (magnons). At temperatures higher than the critical temperature, long range order is lost, but spins will still align locally in patches, allowing for spin waves to propagate for short distances. These waves are known as a paramagnon, and undergo diffusive (instead of ballistic or long range) transport. The concept was first proposed based on the spin fluctuations in transition metals, by Berk and Schrieffer and Doniach and Engelsberg, to explain additional repulsion between electrons in some metals, which reduces the critical temperature for superconductivity. Properties Magnon behavior can be studied with a variety of scattering techniques. Magnons behave as a Bose gas with no chemical potential. Microwave pumping can be used to excite spin waves and create additional non-equilibrium magnons which thermalize into phonons. At a critical density, a condensate is formed, which appears as the emission of monochromatic microwaves. This microwave source can be tuned with an applied magnetic field. See also Magnonics Holstein-Primakoff transformation Surface magnon polariton References Further reading Quasiparticles