I wonder: do there exist "magnetic semiconductors" and magnetic diodes and transistors? Normal electrical semiconductors rely on the fact that there are positive and negative charge carriers. Magnetism does not have monopole charges, so it will not be possible to construct an isolated region of a magnetic semiconductor, but maybe it is possible to have an indivisible magnetic semiconductor junction, in the same sense that you can have indivisible magnetic dipoles despite lack of the monopoles? What is a magnetic analogue of electric potential? Is there something analoguous to electic capacity? Do there exist some laws that forbid existence of magnetic semiconductors? If not, have they been researched or even invented?