Directional control of spin-wave emission by spatially shaped light

In future spintronics it is anticipated that spin waves will function as unique information carriers that are free from Joule heating 1 , 2 , 3 , 4 , 5 , 6 , 7 . Directional control of spin-wave emission has been desired for the realization of switching devices. Here, we propose a promising technique that makes use of a spatially shaped light pulse with circular polarization. Focusing this light pulse on a magnet generates spin waves via the inverse Faraday effect. Moreover, the wavenumber distribution of the spin waves is determined by the spatial intensity distribution of the light spot. We demonstrate the principle of this technique both theoretically and experimentally. We successfully control the direction of the energy flow by shaping the light spot into an ellipse, with its major axis parallel or perpendicular to the magnetic field. Our findings will open up the possibility of fast and arbitrary synthesis of spin-wave patterns by using a more sophisticated light-shaping technique, for example using a computer-generated hologram 8 . Researchers use spatially shaped light to control the direction of spin-wave emission from the ferrimagnetic insulator Gd 4/3 Yb 2/3 BiFe 5 O 12 . They capture the essential features of the observations by employing a simple model that maps the spatial profile of the pump pulse onto the dispersion relation of the spin wave.