Faraday Magneto-optical Properties In Metal-dielectric Composites

The research and study on Magneto-optical effect is of quite significance. On the one hand, Magneto-optical effect can be applied to explain the energy spectrum of crystals, to understand the level structure of magnetization, and to observe the distribution of the intensity of magnetization. On the other hand, with the developments in the field of laser and optoelectronics, Magneto-optical devices have been widely used in magnetic recording, optical communication, and other highly advanced technology. The magneto-optical effect has very important applications in the modern optics as well. Up to now, Faraday magneto-optical effect has a nonreciprocal character, which is of great technical importance. To achieve Faraday rotation angle as high as possible is a major goal in the development of magneto-optical materials. Magneto-optical properties of metal-dielectric composites depend not only on their composition but also on the microstructure.The purpose of our work is to study Faraday magneto-optical properties of metal-dielectric composites for different structure. The main results of our study are listed as follows:1. Faraday magneto-optical rotation in compositionally graded filmsGraded composite materials as new functionally composite materials, which have many novel features in comparison with traditional composite materials, have received much attention. We present a two-step homogenization method to study the Faraday magneto-optical rotation in graded metal-dielectric composite films. First, we adopt effective medium theory to formulate the equivalent (local) dielectric permittivity tensor for a z-slice. Second, the graded composite films are homogenized with effective (over-all) dielectric permittivity tensor including the diagonal and off-diagonal elements. To demonstrate the effects of the graded profile, we have studied Faraday rotation as a function of the graded profile p ( z)= a(z/W)m with the same total volume fraction. For a power-law form with different m, it is found that with increasing m, the magnitude of Faraday rotation becomes weak near the surface plasmon resonant band, accompanied with the red-shift of the resonant center. To one's interest, it is possible to achieve strongly enhanced Faraday rotation in the high frequency region, and to change the direction of the rotation in the low frequency one. Further, the effects of the particles'shape on Faraday rotation are discussed. It is found that the magnitude of Faraday rotation can be further enhanced for needle-like particles. In the dilute limit, we show that Faraday rotation is indeed independent of m within Maxwell-Garnett theory.2. Magneto-optical properties of periodic multilayer filmsWe have derived the general transfer matrix of the propagation of polarized light in one-dimensional anisotropic media based on Maxwell's equations. We investigate the magneto-optical properties of periodic multilayer films which are made of alternating layers of magnetic (M) and dielectric (G) materials. This periodic structure is described as [ MG]n, where n is the repetition number. Our study shows that periodic multilayer films exhibit a very large Faraday rotation because of considerable localization of light. We confirmed that the Faraday rotation (magneto-optical effect) increases with an increase of the repetition number. We also observe some shake peaks in the Faraday rotation angle and transmittance in the high frequency region as a result of the interference effect within the magnetic layer. Furthermore, we find the Faraday rotation is enhanced when the film thickness of the magnetic layer increases. When we decrease the thickness of the magnetic layer and increase the repetition number at the same time, our numerical results are in good agreements with those analyzed by the effective medium theory. The magnetic-optical characteristics of the periodic multilayer films are governed by the degree of localization of light, which can be controlled by varying the repetition number of film structure and the thickness of the magnetic layer.