Spintronics based on magnetic and non-magnetic elemental metals
generated functionalities that are employed in nanoscale devices such as
switches, memories, and sensors. Ferrimagnetic electric insulators such
as man-made yttrium iron garnets form another class of versatile
materials, with supreme magnetic quality. K. Uchida, E. Saitoh c.s.
demonstrated that they can be actuated thermally and electrically and
thereby integrated into conventional electronic and thermoelectric
devices, raising the hope for a new and green spintronics. After an
elementary introduction into the basic physical concepts, I will review a
number of experimental discoveries and theoretical insights on magnetic
insulators and its heterostructures with metals.