Magnetophotonic waveguide nanostructure for selective ultrafast optical excitation of high-K spin dynamics

Optomagnonics provides a promising method of a Joule-loss-free spin control that can be performed at ultrafast timescale. However, the cornerstone of optomagnonics is impossibility to focus the light tighter than a diffraction limit. This constrains minimal size of the optically switched magnetic bits and minimal wavelengths of the optically excited spin waves in optomagnonic devices thus preventing its further progress. Here we propose and experimentally demonstrate a novel method of the selective optical excitation of the short exchange spin waves by using a specially designed magnetophotonic grating. This method is based on the creation of the sign-changing profile of the inverse Faraday effect (IFE) induced in a magnetic film due to excitation of the optical guided TE-mode by a femtosecond laser pulse. The spatial period of the IFE profile is subdiffractive which allows to launch narrow band short spin waves whose wavelengths are around 300 nm as was experimentally demonstrated and potentially can be made down to ~ 100 nm. This opens new horizons for optomagnetic applications that are wide ranging, from logical elements to data processing devices.