the scanning Hall probe Mircroscopy (SHPM) technique, images of the magnetic
modulation can be obtained at the surface of samples with a magnetic response,
like magnetic and superconducting systems. It is a local technique which can
give vital information about the microscopic magnetic mechanisms underlying
the macroscopic or global behaviour of magnetic and superconducting systems.
The working principle of the SHPM technique is based on the incorporation of
a submicron-sized GaAs/AlGaAs heterostructure Hall sensor into a scanning probe
technique. While scanning over a sample surface with magnetic modulation, the
sensor picks up the perpendicular component of the local magnetic field bz(r)
and produces a Hall voltage directly proportional to the field strength. In
this way, a magnetic image of the sample can be constructed. The GaAs/AlGaAs
III-V semiconductor heterostructure Hall sensor contains a two-dimensional electron
gas (2DEG) with a very high mobility, which allows a very high magnetic field
resolution, in the order of 0.1 Gauss at room temperature. The lateral resolution
of this magnetic imaging technique is determined by the size of the Hall cross
and is typically ~700 nm. The major advantage of the SHPM technique is that
it is non-invasive, which is important when the magnetic features of the sample
should not be disturbed, like in the case of unpinned vortices in superconductors.
Furthemore it has a very high sensitivity, it gives direct and quantitative
information about the local magnetic field and the technique is applicable in
externally applied magnetic fields and in a wide temperature range.
At the moment the SHPM system at the VSM laboratory is operational at room temperature.
In the future we will make it operational also at low temperatures, down to
liquid helium temperature (4.2 Kelvin = -269 °C), at which magnetic field
resolutions up to 0.01 Gauss can be obtained.