In essence, spin waves are a propagating re-ordering of the magnetisation in a material and arise from the precession of magnetic moments.
Modern magnetism is concerned with furthering the understanding of the behaviour of the magnetisation on very small (sub-micrometre) length scales and very fast (sub-nanosecond) timescales and how this can be applied to improving existing or generating new technologies and computing concepts.
A magnon torque device was invented and later perfected at the National University of Singapore's Electrical & Computer Engineering department, which is based on such potential uses, with results published on November 29, 2019, in Science.
Small spatial inhomogeneities create an effective macroscopic behaviour, leading to properties not readily found in nature.
By alternating parameters such as the relative permeability or saturation magnetisation, there exists the possibility to tailor 'magnonic' bandgaps in the material.
The damping of the dynamical magnetisation is accounted for phenomenologically by the Gilbert damping constant in the Landau-Lifshitz-Gilbert equation (LLG equation), the energy loss mechanism itself is not completely understood, but is known to arise microscopically from magnon-magnon scattering, magnon-phonon scattering and losses due to eddy currents.
Research in magnetism, like the rest of modern science, is conducted with a symbiosis of theoretical and experimental approaches.
Programs such as OOMMF or NMAG are micromagnetic solvers that numerically solve the LLG equation with appropriate boundary conditions.
[4] Prior to the start of the simulation, magnetic parameters of the sample and the initial groundstate magnetisation and bias field details are stated.
[citation needed] The experimental techniques can be distinguished by being time-domain (optical and field pumped TR-MOKE), field-domain (ferromagnetic resonance (FMR)) and frequency-domain techniques (Brillouin light scattering (BLS), vector network analyser - ferromagnetic resonance (VNA-FMR)).
Time-domain techniques allow the temporal evolution of the magnetisation to be traced indirectly by recording the polarisation response of the sample.
Modern ultrafast lasers allow femtosecond (fs) temporal resolution for time-domain techniques, such tools are now standard in laboratory environments.
By increasing the probe path length, it becomes delayed with respect to the pump beam and arrives at a later time on the sample surface.
This allows to connect ultrafast optics with a local spin-wave excitation and contact free detection in magnonic metamaterials, photomagnonics.