Spin Waves in Ferromagnetic and Antiferromagnetic Materials

A brief outline is given of the spin-wave approximation to the near ground states of ferromagnetism and antiferromagnetism. Simple pictorial models of spin waves are introduced. These models clarify the striking difference between ferromagnetic spin waves, which obey the dispersion law ω ∝ k2, and antiferromagnetic spin waves, which obey the law ω ∞ k. The proper normal modes for antiferromagnetic spin waves are presented. The nature of ferromagnetic and antiferromagnetic resonance is illuminated from a spin-wave point of view.