Mechano- and magneto-optical sensitivity of YIG buffer systems

Abstract

Thin garnet films can be used as magneto-optical sensors or for the realization of optical isolators or modulators in integrated optics. For this purpose, it is desirable to use cheap substrates like SiO₂, instead of, e.g., crystalline Y₃Fe₅O₁₂ (YIG). In the following, we describe the ablation of thin YIG films on SiO₂ substrates (with cuts of (110), (100), (001) and amorphous) using pulsed laser deposition, after which an additional annealing step was used to crystallize the garnet. A previously undescribed anomaly occurred in the produced samples. When measuring the rotation of the direction of polarization (PR) of light transmitting through them, we observed large oscillations in the wavelength spectra of the PR. This did not occur with all types of substrates and depended on the applied magnetic field, but due to the huge rotation angles observed (up to 2° for a 160 nm thin YIG layer), this cannot be ascribed to the Faraday effect (FE). Here, we show that this behavior can be explained by using a simple layer system and taking the birefringence of the substrates into account. TEM images of the real samples were used to set up the layer system, which consists of a thin YIG layer, an intersection area between YIG and the substrate and the crystalline SiO₂. Further investigations concerning the dependence on the magnetic field or the qualitative mechanical tension can be assigned to the proposed model in a satisfactory way, by using a simple mathematical matrix model for layered systems.