Terbium gallium garnet (TGG) single crystal is the most common magneto-optical material used in the visible and near-infrared isolators because of its high Verdet constant, excellent optical transparency and good thermal conductivity. However, it is difficult to grow TGG single crystal due to the serious vaporization of Ga₂O₃ from the molten substances. Moreover, several defects such as color centers, dislocations and inclusions limit the further improvement on the scale of TGG single crystal, which frustrates the application in large aperture-needed Faraday isolator.

Therefore, developing high power Faraday isolators based on magneto-optical ceramics is a promising solution because of the excellent size scalability. In addition, with the development of the transparent ceramic fabrication technology, magneto-optical ceramics exhibit outstanding optical quality compared to that of single crystals. More importantly, TGG ceramics can effectively reduce the volatilization of Ga₂O₃ as its fabrication temperature is lower than the melting point. The overall above factors facilitate TGG magneto-optical ceramics an attractive alternative for the high-power Faraday isolators.

The research team from Shanghai Institute of Ceramics, Chinese Academy of Sciences developed high quality (Tb_0.99Ce_0.01)₃Ga₅O₁₂ magneto-optical ceramics. Polycrystalline (Tb_0.99Ce_0.01)₃Ga₅O₁₂ ceramics were fabricated by the air pre-sintering and HIP post-treatment from high purity powders synthesized via a co-precipitation method. (Tb_0.99Ce_0.01)₃Ga₅O₁₂ ceramics have been characterized by an in-line transmittance of 81.7% at 1064nm. The Verdet constant of the (Tb_0.99Ce_0.01)₃Ga₅O₁₂ ceramics at 633nm was about ？143.4 rad T^？1 m^？1, which was about 7% higher than that of the TGG crystals ( ？134 rad T^？1 m^？1).

This work was published in Scripta Materialia (2019, doi: 10.1016/j.scriptamat.2019.10.023). It was highly appraised by the reviewer, “The ceramic optical quality is excellent and the research content can be a supplement for the development of high-performance magneto-optical materials”.

In recent years, the research team have independently synthesized TGG nanopowders, and strictly controlled the synthesis process to optimize the composition, morphology and agglomeration state of the powders (Optical Materials, 2019, 90: 26-32; Journal of Inorganic Materials, 2019, 34: 791-796). TGG powders were synthesized by the co-precipitation method. The powders showed low-agglomeration and high sinterability, so that the powders compact could be sintered to be transparent by a two-step sintering method. The in-line transmittance of the TGG ceramics is 80.3% at 1064 nm, which is near to the theoretical value. The prepared TGG magneto-optical ceramics show the similar Verdet constant compared to the commercial TGG crystals, published in the Optical Materials (2019, 88: 238-243).

Fig. 1. Photograph and in-line transmittance curves of (Tb_0.99Ce_0.01)₃Ga₅O₁₂ ceramics.

Fig. 2. Photograph and in-line transmittance curves of TGG ceramics.

Reference:

1）https://www.sciencedirect.com/science/article/pii/S1359646219306062

2) https://www.sciencedirect.com/science/article/pii/S0925346719301107

3) http://www.jim.org.cn/CN/10.15541/jim20180574

4) https://www.sciencedirect.com/science/article/pii/S0925346718307900

Contact:

Prof. LI Jiang

Shanghai Institute of Ceramics, CAS

lijiang@mail.sic.ac.cn