Spin hydrodynamic generation

Magnetohydrodynamic generators use magnetic fields to convert the kinetic energy of conducting fluids into electricity. Fluid motion is now shown to generate spin currents, which can induce electric voltages without applying magnetic fields. Magnetohydrodynamic generation1,2,3,4 is the conversion of fluid kinetic energy into electricity. Such conversion, which has been applied to various types of electric power generation, is driven by the Lorentz force acting on charged particles and thus a magnetic field is necessary3,4. On the other hand, recent studies of spintronics5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23 have revealed the similarity between the function of a magnetic field and that of spin–orbit interactions in condensed matter. This suggests the existence of an undiscovered route to realize the conversion of fluid dynamics into electricity without using magnetic fields. Here we show electric voltage generation from fluid dynamics free from magnetic fields; we excited liquid-metal flows in a narrow channel and observed longitudinal voltage generation in the liquid. This voltage has nothing to do with electrification or thermoelectric effects, but turned out to follow a universal scaling rule based on a spin-mediated scenario. The result shows that the observed voltage is caused by spin-current6 generation from a fluid motion: spin hydrodynamic generation. The observed phenomenon allows us to make mechanical spin-current and electric generators, opening a door to fluid spintronics.