Optical coatings for improved contrast in longitudinal magneto-optic Kerr effect measurements

We have studied the increases in the longitudinal magneto-optic Kerr effect signal contrast that can be achieved by the application of optical overlayers on magnetic films. For simple coatings, a factor of $∼3$ improvement in signal contrast is possible. Matching the optical impedance of the magnetic material improves the raw Kerr signal and also reduces the sample reflectivity, yielding a large Kerr angle. The contrast can be optimized by increasing the rotated Kerr reflectivity component while maintaining enough of the base reflectivity Fresnel component to produce a strong signal. Calculations and experimental results are presented for single layer $ZrO2$ dielectric coatings on Ni along with calculations for a three-layer $Au–ZrO2–Ni$ structure. Incidence angle effects are also presented.