Transmission of electrical signals by spin-wave interconversion in a magnetic insulator

Spinning a message An insulator does not conduct electricity, and so cannot in general be used to transmit an electrical signal. However, the electrons within an insulator possess spin as well as charge, so it is possible for them to transmit a signal in the form of a spin wave. Kajiwara et al . have now developed a hybrid metal–insulator–metal structure in which an electrical signal in one metal layer is directly converted to a spin wave in the insulating layer. This wave is then transmitted to the second metal layer, where the signal can be directly recovered as an electrical voltage. The observation of voltage transmission in an insulator raises the prospect of insulator-based spintronics and other novel forms of signal delivery. An insulator does not conduct electricity, and so cannot in general be used to transmit an electrical signal. But an insulator's electrons possess spin in addition to charge, and so can transmit a signal in the form of a spin wave. Here a hybrid metal–insulator–metal structure is reported, in which an electrical signal in one metal layer is directly converted to a spin wave in the insulating layer; this wave is then transmitted to the second metal layer, where the signal can be directly recovered as an electrical voltage. The energy bandgap of an insulator is large enough to prevent electron excitation and electrical conduction 1 . But in addition to charge, an electron also has spin 2 , and the collective motion of spin can propagate—and so transfer a signal—in some insulators 3 . This motion is called a spin wave and is usually excited using magnetic fields. Here we show that a spin wave in an insulator can be generated and detected using spin-Hall effects, which enable the direct conversion of an electric signal into a spin wave, and its subsequent transmission through (and recovery from) an insulator over macroscopic distances. First, we show evidence for the transfer of spin angular momentum between an insulator magnet Y 3 Fe 5 O 12 and a platinum film. This transfer allows direct conversion of an electric current in the platinum film to a spin wave in the Y 3 Fe 5 O 12 via spin-Hall effects 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 . Second, making use of the transfer in a Pt/Y 3 Fe 5 O 12 /Pt system, we demonstrate that an electric current in one metal film induces voltage in the other, far distant, metal film. Specifically, the applied electric current is converted into spin angular momentum owing to the spin-Hall effect 7 , 8 ,