Giant nonlinear Faraday effect in the ferromagnetic semiconductor EuO

Faraday's discovery in 1846 of magnetically induced optical activity has constituted the first conclusive demonstration of the intimate connection between magnetism and light. Since then this so-called Faraday effect and other magneto-optical effects have been playing a vital role in modern technology. It became important to find new materials or novel mechanisms with magneto-optical effects as large as possible. Here we report the experimental observation of nonlinear Faraday effect (NFE) in optical third-harmonic generation (THG) process and a demonstration of the giant enhancement of the NFE in epitaxial film of the ferromagnetic semiconductor EuO. The NFE in THG process is caused by the magnetization-induced term of the third-order optical polarization. We investigated the NFE by the temperature-, magnetic field-, and spectral-dependent measurements and show that the large NFE occurs at 4f7 → 4f65d1(t2g) transitions of Eu2+. It is shown that the NFE can be much larger than linear Faraday effect and its polarization rotation ability exceeds 107 deg/cm in EuO.