Fast ab initio methods for the calculation of adiabatic spin wave spectra in complex systems

The interpretation of the physics of magnets with reduced dimensionality often requires information on the spin wave excitations at arbitrary wavelengths which is generally hard to obtain experimentally. Two powerful methods for the ab initio calculation of adiabatic spin-wave spectra are introduced, a frozen-magnon-torque method for systems with large exchange fields and a transverse-susceptibility method which may be used also for materials with smaller exchange fields. The efficiency of both methods results from the fact that the number of calculations required to obtain the spin-wave spectrum scales linearly with the number of basis atoms in the unit cell. Results are given for Fe, Co, Ni, permalloy Ni₃Fe, and CoFe, materials which are often used for thin-film technologies.