Magneto-Optical Kerr Effect User Instrumentation

The Magneto-Optical Kerr Effect probe (MOK3) was designed and built by Dr. Wilhelmus J. Geerts (now at Southwest Texas State University in San Marcos) to be used in the 50 mm bore magnets at the Magnet Lab in Tallahassee. MOK3 can be used to carry out magneto-optical measurements on thin films, transparent materials, liquids and gasses in fields up to 20 tesla (or 25 tesla if the project is given time in the Keck magnet), and at temperatures from 2 K to 325 K. Typical sample diameters are between 0.5 cm and 2 cm. MOK3 has a rotation noise level of less than 0.5 mdegrees on bulk iron, and a residual system background smaller than 2 mdegrees/tesla. A better signal to noise ratio and lower system background are obtained for the ellipticity signal.

The light source for the MOK3 is a HeNe laser (632 nm). The wavelength window of the optics is 325 to 1600 nm. Although other cylindrical (external power supply) lasers can be used in MOK3, the laser light source can not be replaced by a lamp.

The equipment, the first of its kind, is designed to be as multifunctional as possible. Its modular structure allows modifications and the insertion of user-dependent sample holders. For users interested in designing their own sample holder, a technical report is available that includes a service manual, design rules and reasons, addresses, references and the technical drawings. This information can be downloaded from the links below.

• The MOK3 manuals in postscript (stuffed binary, 1.3 MB)
• The MOK3 manuals in postscript (zipped, 1.3 MB)
• "On the design of a Magneto-Optical Kerr probe for measurements in high fields and at low temperatures" by W. Geerts (pdf, 6.1 MB)
• "MOK3: User Manual" by W. Geerts (pdf, 4.7 MB)

Magneto-Optical Kerr Effect Example Data

At room temperature the MOK3 instrument can be used to determine saturation fields for ferromagnetic films. In the following figure, raw data taken with the MOK3 is shown for a sample of SmCo film and for a Si substrate without the subject film. Part of the background signal is associated with the effect of the magnetic field on the instrument. It is necessary to run a background check and subtract this from the measured data with the sample in place.

Below, the background and substrate signal has been subtracted from the SmCo film to leave the Kerr rotation due to the SmCo film.

For more information, please contact Interim DC Program Director Tim Murphy.