Principles of switching elements that use the variation of propagation properties of gyrotropic waveguides caused by changes in the orientation of the applied d.c. field are outlined. It is shown that packing densities comparable with magnetic-bubble devices (25 μm per cell) are readily obtainable and that applied magnetic fields and associated d.c. currents can be quite small, giving rise to minimal heat dissipation. Switching speeds in the nanosecond range are expected.