Focusing and Caustics of Magnons in Ferromagnetic Semiconductors with FCC Structure

Directions of the focusing of exchange spin waves inside crystals with an FCC lattice of the rock-salt type are determined. Using the example of ferromagnetic semiconductors EuO and EuS, it is shown that neither an external magnetic field nor dimensional effects are required for focusing in such systems. The directions in the crystal and the necessary conditions for the formation of magnon caustics are determined.