App. Note: Magneto-optic Investigations with the Aurora NSOM

Application Note:
Magneto-optic Investigations with the Aurora NSOM

A. Englisch and Prof. U. Hartmann; Experimental Physics Department, University of Saarbrücken, Germany

Magneto-Optical NSOM on a YSmBiGaFe garnet film (Fig. 1 - left, Fig. 2 - right)

The Aurora Near-field Scanning Optical Microscope permits magneto-optical investigations to be performed in the near-field as well as far-field regime. For this purpose, a standard Aurora (tm) at the University of Saarbrücken was equipped with an optical phase shifter, a precision analyzer, and as induction coil which produces magnetic fields oriented perpendicular to the sample plane. On various samples, magneto-optic images were obtained in transmission and reflection.

In the near-field mode of operation, a lateral resolution well below the wavelength of the employed laser (488nm) was achieved. The images presented (both 20µm x 20µm) show magnetic domain contrast on a YSmBiGaFe garnet film of uniaxial anisotropy observed in transmission. Figure 1 shows the arrangement of the oppositely magnetized domains in the absence of an external magnetic field. Figure 2 shows the same area under the influence of an AC modulation field which excites vibration of the domain walls.

Employing phase and frequency-dependent detection of the Aurora photomultiplier signal, local variations of the domain wall mobility can by analyzed. Thus, it is possible to study in detail pinning mechanisms and relations between structural defects and magnetism. Since the topography of a sample can be simultaneously detected in terms of the shear force image, the Aurora is a powerful tool for the examination of the interplay between crystallographic structure and magnetism at a sub-micron scale.