A NEW FARADAY-ROTATION GLASS WITH A LARGE VERDET CONSTANT

Heavily terbium-doped boron-silicate glasses (Tb3+ 10.4 at. %) with a Verdet constant (632.8 nm, room temperature) as large as -0.338 min/Oe cm, 38% larger than that of the famous FR-5 glasses, have been made. The wavelength and temperature dependencies of the Verdet constants of samples have been investigated in the ranges of 400 to 800 nm and 100 to 300 K. The results show paramagnetic Faraday rotations. The measur ed susceptibilities between 77 and 300 K support this point but with a n effective Bohr magneton number 7% smaller than the theoretical value for free Tb3+ ions. Susceptibilities are further measured at temperat ures from 1.5 to 100 K and magnetic fields from 0.2 to 5.0 T. The resu lts show saturation of magnetization and give a Neel temperature of ab out -9 K. The effective Bohr magneton number in the state of saturated magnetization is 55% smaller than the free ion value. These results m ay indicate the single ion anisotropy reduction of the magnetization o f the disordered Tb3+ ions at low temperatures. The measured indices, Abel number, and nonlinear-index coefficient are 1. 745 92 (N(C)), 1.7 46 70 (N632.8), 1.749 84 (N(D)), 1.760 31 (N(F)), 49.92, and 7.638 x 1 0(-20) m2/W, respectively. The transmittance of the sample (15.2 mm th ick) is up to 85% in the range from 400 to 1500 nm. It is known that t he lower transmittance is mainly due to Nd3+ and Pr3+ impurities in th e raw material TB4O7 by optical absorption analysis.