Faraday Rotation and Gyromagnetic Effects of Trivalent Europium Ions

The electronic magnetization of Eu3+ ions at low temperatures is associated with Van Vleck temperature-independent paramagnetism; the ground state has J=0. We have calculated the Faraday rotation for this ion. A contribution from the Van Vleck paramagnetism is partially cancelled by the usual diamagnetic term. The resulting rotation should be observable in Eu3+ in the microwave and infrared regions. In the appropriate limits we find for the rotation per unit length Δθ/Δx=(48μB2N/ℏν)(ℏω/Δ)4(μBH0/Δ)[1−(ℏω/Δ)2]−2,where N is the concentration, v is the velocity of light in the medium, and Δ is the splitting between J=1 and J=0. We give the appropriate modification of this formula in a crystal field. We calculate the gyromagnetic ratio g′; at low temperatures the calculations of Frank have to be corrected to take into account nuclear effects.

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