A 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. To measure the in-plane magnetization, an oblique angle incidence must be used. However, in this oblique angle configuration, the measured signal has contributions from both the polar and longitudinal MOKE responses [1]. The polar and longitudinal MOKE have different dependences based on the direction of the incidence beam, because the in-plane magnetization breaks the mirror symmetry about the xz plane, while the out-of plane magnetization retains the mirror symmetry [2]. To suppress the polar Kerr signal, we demonstrate a technique using a mirror to reflect the beam back on to the sample. By selectively using a quarter-wave plate, we take advantage of the different dependencies of the MOKE response to independently suppress the polar MOKE signal. Therefore, the longitudinal and polar Kerr effects may be studied separately using the same experimental setup. To demonstrate the feasibility of this technique, we use an out-of-plane magnetized Pt/Co/Pt film as well as a Pt/Co/Cu/NiFe heterostructure with both in-plane and out-of-plane magnetization. The out-of-plane Pt/Co/Pt hysteresis measured with our technique suppressed the polar MOKE signal 10 times when compared to a conventional MOKE measurment. By accounting for the impact of birefringence via tuning the incident polarization with a half-wave plate, we can fully suppress the polar MOKE response in the oblique angle incidence, while enhancing the longitudinal MOKE signal of the Pt/Co/Cu/NiFe structure when compared to a conventional MOKE measurement. The suppression we observe by tuning the half-wave plate results in more than 160 times of suppression [3]. We expect this convenient technique to improve the sensitivity and capability of MOKE based magnetometry

[1] J. Zak, E. Moog, C. Liu, Physical Review B., Vol. 43, p.6423 (1991)

[2] H. Ding, S. Pütter, H. Oepen, Journal of Magnetism and Magnetic Materials., Vol. 212, p.5-11 (2000)

[3] R. Greening, E. DeVisscher, X. Fan, "A method to suppress polar Kerr signal in a longitudinal magneto optic-Kerr-effect measurement" in preparation