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Ferromagnetic resonance (FMR) measurement was performed at the frequency of 9.8 GHz and at the room temperature on a series of Fe-SiO2 granular films fabricated by the Ar+-beam sputtering technique. Our results indicated that when the iron volume fraction (fv) of the films exceeds 0.28, the FMR spectra are superpositions of volume modes and surface modes. The analysis on the effective anisotropy field suggests that the intrinsic anisotropy (including the volume and interface one) becomes maximal when fv near the percolation threshold (fp). In particular, it was found for the films with fv=0.42 that the spin wave resonance modes satisfy the relation Hres∝n with a separation field of about 174 Gs between the successive modes. Our study reveals that Fe particles are coupled by a yet unknown interparticle interaction when fv is just below fp.

Vortex beam carrying orbital angular momentum (OAM) is disturbed by oceanic turbulence (OT) when propagating in underwater wireless optical communication (UWOC) system. Adaptive optics (AO) is a powerful technique used to compensate for distortion and improve the performance of the UWOC system. In this work, we propose a diffractive deep neural network (DDNN) based AO scheme to compensate for the distortion caused by OT, where the DDNN is trained to obtain the mapping between the distortion intensity distribution of the vortex beam and its corresponding phase screen representing OT. In the experiment, the distorted vortex beam is input into the DDNN model where the diffractive layers are solidified and fabricated, and the intensity distribution of the modulated light field of the vortex beam can be recorded. The experiment results show that the proposed scheme can extract quickly the characteristics of the intensity pattern of the distorted vortex beam, and the predicted compensation phase screen can correct the distortion caused by OT in time. The mode purity of the compensated vortex beam is significantly improved, even with a strong OT. Our scheme may provide a new avenue for AO techniques, and is expected to promote the communication quality of UWOC system immediately.