Garnets with high magnetooptic figures of merit in the visible region

This paper describes the effects on Faraday rotation and optical absorption of substituting bismuth into various single crystal iron garnets. The large negative contribution to the Faraday rotation produced by the presence of bismuth is of the diamagnetic form and is associated with an optical transition around 415 nm. The magnitude of the bismuth contribution depends on the concentrations of bismuth and tetrahedrally coordinated Fe ³⁺ ions, suggesting that both these ions are involved in the transition responsible for the additional rotation. The absorption arising from the bismuth increases with decreasing wavelengths. However, the increase in magnitude of the rotation is such that the figure of merit is increased above that of YIG, peaking at 560 nm with a value of 5.2 deg/dB. The Faraday rotation and figure of merit of low magnetization garnets, suitable for magnetooptic devices, are also increased in the visible by the presence of bismuth.