Magnetooptic
Kerr Effect
In
our experiment, a
birefringent photoelastic modulator (PEM) modulates the reflected laser
beam, in order to separate the polarization components of rotation and
ellipticity in the reflected beam using lock-in
techniques. Both
components are proportional to the magnetization in the sample.
By
sweeping the applied magnetic
field, the magnetic
behavior of the sample can be characterized, e.g. hysteresis loops of
ferromagnetic materials.
Temperature
can also be varied between 500K and liquid
nitrogen temperature (77K) using a heater and a Joule-Thomson
microrefrigerator
in a sample vacuum chamber.
 For combinatorial samples, the
MOKE
response as a function
of position on the sample can be measured either by scanning a focused
laser
beam (typically 100 microns in diameter) or by imaging using a CCD
camera.
Magnetic properties, e.g. Curie temperatures and coercive fields, can
be
determined as a function of composition.
A
MOKE Map. Magnetism
at room temperature
as a function of alloy compositions. The corners of the triangle
represent pure
manganese (Mn), pure cobalt (Co), and pure germanium (Ge). |
