Research Facilities
Surface Magneto Optic Kerr Effect (SMOKE)
The SMOKE is a probe for studying surface and ultrathin film magnetism with submonolayer sensitivity. This technique was pioneered by S.D. Bader and E.R. Moog in the late '80's for measuring magnetic hysteresis loops from ultrathin ferromagnetic films (Moog, E.R. and S.D. Bader. "Superlattices and Microstructures" Vol. 1:543 1985).
We have designed and built our own SMOKE setup by consulting Liz Moog at the initial stage of development in 1990. The physical principle of SMOKE is that when plane polarized light is incident on a magnetized material, the plane of polarization of the reflected light is rotated with respect to the plane of polarization of the incident light. The theoretical explanation of the Kerr effect is that the index of refraction of the right-handed circularly polarized light and the index of refraction of the left-handed circularly polarized become different when a material is magnetized. Any plane polarized light can be decomposed into two circularly polarized light. The magnitude of the rotational angle of the Kerr effect for a ferromagnetic material is generally between 10E-4 to 10E-3 degrees, (although large rotation angle materials have been found in Tb-Fe-Co metal alloys (one degree) and uranium compounds (nine degrees)). The angle of rotation is more pronounced when the incident angle is increased. The magnetization of a sample can be changed and switched by an applied magnetic field. The detected change in the Kerr intensity (which is proportional to the Kerr rotation and to the sample's magnetization) versus the applied magnetic field gives the hysteresis loop. A schematic of the SMOKE apparatus is shown below.
(1) Laser, (2) polarizers, (3) mirrors, (4) sample, (5) magnetic core, (6) pulley, (7) photodetector, and (8) band-pass filter. This diagram is the measurement of longitudinal Kerr Effect and the external field is in the plane of smaple. The electromagnet can be rotated by means of the pulley through a push-pull rod.
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