The optical input bench of the MOKE measurement apparatus ( see below) consists of a laser diode (Sanyo DL3147-041, 5 mW) operating at λ=645nm (≈2eV)which is power stabilized and temperature controlled ensuring a highly stable light intensity.

An aspheric lens focuses the linear s or p polarized light, i.e. perpendicular or parallel to the plane of incidence respectively on the surface of the sample. The incidence of the light with respect to the sample surface normal is typically set at 35°.

After reflection, the beam passes though a Photo-Elastic Modulator (PEM: quartz bar vibrating at 50 kHz) with its major axis perpendicular to the plane of incidence providing a time-dependent phase shift between the s and p components of the elliptically magneto-optical induced response.

An analyzer and a lens collect the signal on a low noise amplified silicon photo-detector connected to a lock-in amplifier. This experimental set-up has main advantages :

• it provides a highly sensitive detection system, since the high-frequency ellipticity modulation ensured by the PEM moves away the signal from the low-frequency noise which limits the signal to noise ratio;

• the detected signal IKerr at the fundamental modulation frequency (twice) is proportional to the magneto-optical Kerr ellipticity εK (rotation θK).

The sample is mounted at the center of a four-mutually orthogonal-homemade coils system. Our coil configuration permits one to apply static fields up to 3500 Oe in any direction of the film-plane and in particular to apply a longitudinal (in-plane of incidence) and/or transverse field.