Enhancement of Faraday effect of transparent ferromagnetic Co‐MgF₂ granular film by introducing Fabry–Pérot resonant structure

Abstract

To detect the magnetic field using polarization of a light, transparent magnetic material having a Faraday effect is required. The Co-MgF 2 granular film is promising as a candidate of the Faraday element for the magnetic field sensing. In this study, Fabry-Pérot resonant structure was introduced into the Co-MgF 2 granular film to enhance the Faraday effect. It was found that the Faraday effect per unit film thickness [deg/ m] was enhanced due to a light localized in the Co-MgF 2 granular layer sandwiched by Bragg mirror of the insulator multilayer. The maximum Faraday effect of the proposed structure was −1.24 • / m, which was about 3.4 times enhancement compared with a single Co-MgF 2 film, when the number of layer period x in Fabry-Pérot resonant multilayer was 5, where the structure was substrate/(Ta 2 O 5 /SiO 2 ) x /Co-MgF 2 /(SiO 2 /Ta 2 O 5 ) 2 /Air. Furthermore, the multicavity structure, consisting of the Fabry-Pérot resonant multilayer film continuously placed, exhibited a 50% increase of figure of merit (FOM) defined as Faraday rotation angle per transmission loss [deg/dB]. K E Y W O R D SFabry-Pérot resonance, Faraday effect, ferromagnetic, granular thin film, multicavity Electr Eng Jpn. 2019;206:3-10.