Large longitudinal Kerr rotations and figures of merit in thin Iron films

The longitudinal Kerr effect in thin iron films prepared by electron-beam evaporation on glass substrates has been studied as a function of film thickness (20-1340 Å), angle of incidence (30-75 degrees), incident index of refraction (1-1.65), and wavelength (0.4-0.8 μ) with
p
and
s
incident polarizations. In addition, the Kerr figures of merit were determined from the measured values of the double Kerr rotations and optical reflectivities. The film thickness was measured by interferometry and X-ray fluorescence techniques. As the film thickness decreased, the magnitude of the Kerr rotations with
p
and
s
polarizations decreased from about 8 minutes to zero for an incident index
n_{1} = 1
, an exit index
n_{3} = 1.52
, and a 45- degree angle of incidence. However, the rotations of the same films increased from about 16 minutes to a maximum of 30 minutes near 200 Å for
n_{1} = 1.52 , n_{3} = 1
, and a 45-degree angle of incidence at the film surface. The corresponding Kerr figures of merit for
n_{1} = 1.52
exhibited peaks about a decade larger than the values determined for
n_{1} = 1
. Clearly, a simple increase of the incident index of refraction provides a significant enhancement of a magnetooptical signal. Analysis of the phenomenological magnetooptical equations for a two-surface thin-film structure gives satisfactory agreement with our results.