Magneto Optic Kerr Effect (MOKE) Measurements

DESCRIPTION

The Magneto-Optic Kerr Effect (MOKE) describes changes to light reflected from a magnetic surface. These changes result from the off-diagonal components of the dielectric tensor. These off-diagonal components give the magneto-optic material an anisotropic permittivity, meaning that its permittivity is different in different directions. 

There are two main types of MOKE measurements. Transverse/Longitudinal MOKE to detect in-plane magnetization and Polar MOKE to detect out-of-plane magnetization.

The experimental setup consists of:

• An electromagnet with bipolar power supply to generate the magnetic field

• A polarized light source for probing the sample's magnetization

• A photoelastic modulator to periodically modulate the light between left and right circularly polarized light

• A photo detector to detect the reflected light from the sample

• A lock-in-amplifier to improve the signal to noise ratio

• A GPIB card to control the magnetic power supply and the lock-in amplifier through the computer

Each sample is loaded into the custom MOKE fixture.  This fixture enables the sample to be tested per ASTM standard D6272 [Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials by Four-Point Bending].  

This test results in Kerr rotation and Kerr ellipticity measured at different fields.  These measurements are used to produce a hysteresis loop. By measuring the change in M vs H loops with the applied strain one is able to calculate the coupling between magnetic and mechanical fields and estimate the magnetostriction values.  Therefore resulting in a measurement of the magnetostriction in thin magnetic film structures.  This technique can be used for the following studies

• Magnetic Nanostructures

• Magnetostriction 

• Exchange-bias 

• Spintronics

REFERENCES

• https://doi.org/10.1063/1.5007655

• https://doi.org/10.1063/1.5006676