Oblique incidence of light propagation in magnetic anisotropic media and digital photonic device applications

In this presentation, we demonstrate an interesting physics about spin reorientation transition of the magnetic Co ultrathin films (up to ~ 2 nm) on ZnO crystal. The behavior has been observed by surface magneto-optic Faraday effect (SMOFE) magnetometry. SMOFE hysteresis measurement in ultrahigh vacuum (UHV) can be accomplished for investigating the magnetic properties of ultrathin films that is deposited on a transparent substrate. Through the doping of N ions into the top Co structure, nitrogen implantation is conducive to stabilize the surface magnetism. The magneto-optic vector magnetometry during the growth of Co was monitored. The magnetization with certain thickness oscillates with incident optical angle. The phenomenon is attributed to the multiply-reflected beams and optical interference in the dielectric crystals. By tuning the incident angle of light, magnetic reversal flips spin-up state, i.e. the digital signal is denoted as "1", to spin-down state, denoted as "0". The effect is a fundamental basis for the application of digital photonics device. The longitudinal anisotropy is dominated in the initial growth of Co due to large lattice misfit between the thin film interfaces. However, the easy axis of thin film magnetization rotates gradually to out-of-plane up to 2.3 nm. The technique in applied optics combined thin film technology with SMOFE magnetometry is possible to develop digital signal generation via the mechanical rotation of optics in magnetic thin films.