Method to Suppress Polar Kerr Signal in a Longitudinal Magneto-Optic Kerr Effect Measurement

The magneto-optical Kerr effect (MOKE) is a convenient technique to study the magnetization of thin films. However, both polar and longitudinal MOKE responses contribute to the total Kerr response in a typical longitudinal MOKE measurement. Here, we present a simple optical technique to suppress the polar MOKE response in the oblique angle incidence by exploiting differences between polar and longitudinal MOKE responses upon double reflection from the sample. By using a mirror to reflect the beam and by selectively using a quarter-wave plate, the polar or longitudinal MOKE signals can be suppressed and, therefore, studied separately using the same oblique experimental setup. To demonstrate the feasibility of this technique, we use an out-of-plane magnetized Pt/Co/Pt film and a Pt/Co/Cu/NiFe heterostructure with both in-plane and out-of-plane magnetization. We show that the polar MOKE of the CoPt film can be suppressed by a factor of 6 compared to a conventional MOKE measurement. By accounting for birefringence, we further reduce the polar MOKE response in a longitudinal MOKE measurement of the Pt/Co/Cu/NiFe film by over 160 times compared to a conventional oblique-angle MOKE measurement.