Optical sensing of magnetic field based on magnetorefractive effect in manganites

We have investigated the transverse magneto-optical Kerr effect (TMOKE) in thin films of ferromagnetic manganites (La2/3Sr1/3MnO3, La2/3Ca1/3MnO3) with visible light. In addition to the standard transverse MO Kerr effect - which is proportional to the magnetization component perpendicular to the plane of light incidence - we have observed a strong even contribution roughly proportional to the absolute value of applied magnetic field. It is well observed near the Curie temperature. This contribution is not the ordinary quadratic magneto-optical effect it but is related to the magnetorefractive effect (MRE) - the optical equivalent of magnetoresistance - which give rise a significant change of reflectivity with the applied magnetic field. This magnetorefractive effect can exceed more than ten times the linear magneto-optical effect (MOE). This finding is against common assumption that MRE is negligible in the visible spectral range and therefore both MRE and MOE should be considered. Detailed analysis of measurements in various magneto-optical configurations is provided and the method of separation of both contributions is shown. Finally we envisage the possibility to exploit this effect in remote optical magnetic field sensor, which can be useful for nondestructive, noninvasive, and local magnetic field sensing.