Introduction to antiferromagnetic magnons

The elementary spin excitations in strongly magnetic materials are collective spin deviations, or spin waves, whose quanta are called magnons. Interest in the experimental and theoretical investigation of magnons attracted many groups worldwide about 4–6 decades ago and then waned for some time. In recent years, with the advent of the field of spintronics, the area of magnonics has gained renewed attention. New phenomena have been discovered experimentally, and others have been predicted theoretically. In this tutorial, we briefly review the basic concepts of magnons in antiferromagnetic (AF) materials. Initially, we present a semiclassical view of the equilibrium spin configurations and of the antiferromagnetic resonance in AF materials with two types of magnetic anisotropy, easy-axis and easy-plane. Then, we present a quantum theory of magnons for these materials and apply the results to two important AF insulators, MnF2 and NiO. Finally, we introduce the concept of antiferromagnetic magnonic spin current that plays a key role in several phenomena in antiferromagnetic spintronics.