Turn on the switch
Because the MI effect is changing of AC resistance (impedance), the output of the MI sensor depends on atmospheric/sensor temperature.
To avoid the thermal drift, the main switch of the control unit should be turned on 1-2 hours befor scanning.
Thermal drift
The causes of the thermal drifts are temperature shifts of both atomospher and amorphous wire of the MI sensor itself.
Following magnetic images of same magnetites' SIRM show the effect of the thermal drift. The results indicate that 1 hour aging after turned on the switch and closed the magnetic shield can decrease the thermal drift.
Fig.1 is a magnetic image of 30 minutes after switched on and closed the magnetic shield. The image shows thermal drift as white->red gradations, indicating decreasing of the output voltage with temperature.
On the other hand, Fig. 2 shows the result after 1 hour ageing, showing slight thermal drift.
Fig.1 Magnetic image of SIRM of magnetite single crystals (100^200 um in diameter) showing a moderate thermal drift. (upper) Plot in absolute value mode. (lower) Plot in relative value (high contrast) mode.
Fig. 2 Magnetic image of the same sample without thermal drift.