Magnetically ordered, electrically insulating materials pave the way towards novel spintronic devices. In these materials the flow of magnetic excitations such as magnons results in pure spin currents. These spin currents can be driven by gradients of the spin chemical potential and/or temperature such that they can play the same role in novel spintronic devices as charge currents in traditional electronic circuits. Connecting spin current based and charge current based devices requires spin to charge interconversion. This has been achieved by the spin Hall effect with an efficiency of several 10%. The recent progress in materials development and understanding of pure spin current physics opens up a plethora of novel device concepts and opportunities for fundamental studies.
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