Simultaneously enhancing the optical transparency and Verdet constant of Tb-based magneto-optical ceramic via defect elimination

Defects induced by air annealing pose a serious challenge to simultaneously achieve high transparency and high Verdet constant in Tb-based ceramics. Herein, an efficient strategy of air annealing followed by vacuum re-annealing is introduced in response to the dilemma. For the illustrative example, after a sequence of annealing treatments, the in-line transmittance of Tb₂Hf₂O₇ ceramics was elevated from 59.1 % to 71.2 % at ∼1440 nm, accompanied by significant increase in the Verdet constant (from -280 ± 3 rad·T⁻¹·m⁻¹ to -307 ± 4 rad·T⁻¹·m⁻¹ at 515 nm and -164 ± 2 rad·T⁻¹·m⁻¹ to -181 ± 3 rad·T⁻¹·m⁻¹ at 635 nm). This improvement was achieved through the elimination of defect clusters and antisite defects within the ceramic without introducing excess detrimental oxygen vacancies. The innovative strategy demonstrated here for Tb based ceramics to simultaneously enhance the optical transparency and Verdet constant may open up a path for developing high-performance MO materials for Faraday isolators.