Magneto-Optical Kerr Effect

MOKE(Magneto-Optic Kerr Effect)
When the linear polarized light is reflected from the magnetized material the polarization is changed by the kerr angle and kerr ellipticity.

Faraday Effect vs MOKE
Faraday effect is the transmission case where Kerr effect is the reflection (They have same physical origin and same geometry ).

Physics Origin of MOKE

The origin of the MOKE is came from spin-orbit interaction and exchange interaction. A linear polarization can decompose left and right circularly polarized light(LCP, RCP) and the different interaction between left circularly polarized light and right circularly polarized light with magnetic material change the polarization state after reflection. (We need magnetic field to magnetize the sample).

Experimental Setup Visible Range ( 1.4 - 5.4 eV )

• Light source : 75 W Xenon arc lamp
• Monochrometer : Mcperson 1/4 meter monochrometer
• Polarizer : Calcite G-T
• Modulator : Hinds PEM80 modulation freq. is 50 kHz
• Rotation states : Newport MM80 micro motion controller and micro step motor can control the polarizer rotations with 1/1000 deg resolution.
• Mirrors : UV enhanced Al mirrors with MgF coating.
• Temperature range : N2 + He cooled cryostat with (Room temp - 4.2 K)
• Magnetic field (0-7 T) superconducting cryostat.
• Lockin Amps : Stanford Research SR510 , SR 830 Lockin amps

Light source is Xenon Arc lamp. And calcite polarizer and DC motor can control 1/1000 deg to control exact position of the polarizers. Also using Piezoelectric modulator (PEM) which modulate light at 50kHz at various photon Energy range. Also 7 T Superconducting magnet with Temperature range 2-300 K is used.

Experimental Setup IR Range ( 0.3 -1.4 eV )

For IR range , in principle, all experimental setup is same to visible MOKE. But IR(mid-Infrared) Set up is quite challenging because you cannot see IR without viewer and there are a few optical components for IR range.

First of all You cannot use calcite prizm because of its spectrum cutoff is 2.3 eV. And Xenon Arc lamp is not suitable for IR. And Need special window for IR like LiF, MgF.

• Light source : Should have a peak in MID-IR range and have no cutoff from tube.
• Tried IR Lamps : Halogen lamp  Tungsten lamp  Globar  solac arc lamp
• Polarizer : Wire Grid, Calcite,  TiO2(Rutile), VO4
• Modulator : LiF, CaF based material which has transmittance in IR
• Detector : InSb cooled with N2 at 77 K