Figure 1: Transformation by Kerr effect of a wave polarized linearly into an elliptic wave after reflexion on a magnetized medium.
The Kerr effect under ultra vacuum (SMOKE: Surface Magneto-optic Kerr Effect) results from the interaction between an electromagnetic wave polarized linearly and a magnetized medium. The considered wave is then polarized elliptically (figure 1).
One defines two angles allowing to characterize the elliptic polarization of the light: Kerr rotation (θK) and the Kerr ellipticity (εK). One can show that these two parameters in the case of magnetic thin films are proportional to the magnetization and to the film thickness. An experiment consists in measuring the rotation or the ellipticity according to the intensity of an external field applied in a definite direction that gives an hysteresis loop (figure 2).
Figure 2: Example of hysteresis loop obtained on 8 MC Co/Cu (115).
Figure 3: Two configurations for the Kerr effect measurement.
In our experiment, we can carry out the experiments in two configurations: longitudinal Kerr effect and polar Kerr effect (figure 3).
The experimental setup (figure 4) comprises an ultra-high vacuum chamber (base pressure of 2 10-10 mbar) in which is the magnet. The maximum field being able to be applied is of 1500 Oe with 10 A in the coil. The source of light is a laser diode (wavelength 670 Nm and power of 3 MW, the beam is thought of 45° on the surface of the sample and the detection of the signal is done with a photodiode). The sample can move around a vertical axis in order to pass from the polar configuration to the longitudinal configuration. It can moreover turn around an azimuth axis.
This chamber is connected to a MBE growth chamber in order to study in situ the magnetic properties of the samples.
contact: Helene MAGNAN