Confined magnons

The common belief is that excitations of magnets are always deconfined ``bulk'' spin waves spread out in space, whose quanta called magnons. In reality all materials have surfaces and interfaces break translation symmetry, giving rise to confined them, addition the ones. conditions for existence these magnons still unknown. authors show extra magnetic anisotropy at surface or interface plays a key role magnon confinement, obtain characteristic length scale their spatial localization. Calculations spin-scattering function how can be observed with neutron, electron, photon scattering experiments wide variety materials. accompanying image shows heat map energy versus wave vector ferromagnetic antiferromagnetic appears as flat dispersion (delocalized $q$ localized real space) below lowest bulk mode.