Improvement to the exchange field acting upon Tb3+ ions in TbIG

The spin fluctuations of the magnetic ions play an important role on the magnetic properties of the crystals and lead to a new mechanism for the Curie–Weiss susceptibility. The exchange field Hexch acting on the rare-earth ions in Tb:YIG is improved based on the temperature dependence of the spin fluctuations, which is expressed as Hexch=n0(1+γT+βT−2)MYIG. By means of the improved exchange field, the magnetic and magneto-optical properties of Tb3+ ions in Tb:YIG are calculated. The calculated results are in good agreement with the measured data in the temperature range from 40 to 300 K.