4. SQUID microscopy or magnetometer
The typical
ultimate field sensitivity of the SQUID
microscope is given by the SQUID flux noise divided by the effective
pickup
area. For typical value [4] of flux noise of 
,
a pickup area of 
corresponding to an
effective noise of 
,
where as a pickup
area of 
corresponding
to an effective field noise of
. In the case of scanning
SQUID microscope the pickup coil is few millimeter and it can be
classified by
the temperature in which the SQUID and the sample are placed. Basically
of two
types one with low temperature either in a common vacuum space or in a
cryogenic fluid. And in the second one the SQUID is placed in between
Cryogenic
reservoir and the room temperature. Depending up on the samples both
microscopes
has their own advantages [4]. The images are just the translation of
magnetic
field that scanned over a surface of sample. So the images are usually
false-color or grey scale images.
In
the above figure Dr.J.R.Kirtley [4] has used a Squid microscope to scan
a
Josephson vortex in La-Sr and in some organic crystal when the
temperature was
lowered through Tc. At the temperature close to Tc
the
bright part in the Figure 4.1 spreads out.