Advances in coherent magnonics

Magnonics addresses the dynamic excitations of a magnetically ordered material. These excitations, referred to as spin waves and their quanta, magnons, are a powerful tool for information transport and processing on the microscale and nanoscale. The physics of spin waves is very rich, ranging from a coexistence between dipole–dipole interaction and symmetric and antisymmetric exchange interaction, to various types of interface effects, anisotropies and spin torques. Spin waves are easily driven into the nonlinear regime. They can be confined and guided, and they can be amplified. Spin waves may be generated with varying degrees of coherency, depending on the excitation method, and transport mechanisms range from diffusive to ballistic. In this Review, we address specifically coherent spin waves. Coherency enables, for instance, the design of interference-based, wave processing spin-wave devices. Thus, the field of magnonics is well suited for the implementation of wave-based computing devices, combining the excellent versatility, smallness, nonlinearity and external control it affords. Novel coherent states of matter, such as magnon Bose–Einstein condensates, enable a broad range of additional applications.