Spin waves in antiferromagnetics

A spin wave in a magnetic material is like an acoustic wave in a solid. It is characterized by means of the three general values: the frequency, the wavelength and the lifetime or the mean free path. The frequency of the spin wave is determined by the energy of the interaction of magnetic moments with each other (the energy of the exchange interaction and the energy of the anisotropy) and the energy of the interaction of the external magnetic field. The field dependence of the magnetic energy determines the spectrum of the antiferromagnetic resonance (AFMR); AFMR may be considered as a spin wave of infinite wavelength. AFMR is studied by means of the observation of the microwave power absorption in samples. Using parametric resonance it is possible to excite spin waves with wavelength about 0-1 μm by a microwave source. The part of the spin wave energy which is associated with the exchange energy, and the lifetime of spin waves which in favourable cases reaches 1 μs, are determined in such experiments. An experiment on the direct observation of spin waves propagated along an antiferromagnetic rod is described at the end of the article.