Terahertz Faraday effect in single molecule magnets

Faraday rotation in the terahertz frequency range was observed in molecular magnetic systems. The effect is strongest near the magnetic resonance of the single molecule magnet Mn12Ac at nu=300 GHz, where the Faraday rotation exceeds 150 degrees/mm. Below the magnetization blocking temperature, the effect was observed in the magnetized state of the sample in zero field. Surprisingly, it could even be detected in nonmagnetized states, applying small magnetic fields (H <= 1 T), that do not create net magnetization of the sample. All observations were quantitatively explained without fit procedures using known Mn12Ac spin-Hamiltonian parameters.