Magnetic field calibration of a transmission electron microscope using a permanent magnet material

A new method of assessing the magnitude of the magnetic field in a transmission electron microscope using a permanent magnetic material is described. The approach is versatile and simple enough to be implemented for certain scientific or engineering situations in which the exact calibration of the magnetic field in the microscope column using a small Hall probe may be a problem. We have applied this approach to obtain the magnetic field calibration inside a JEM 3000F field emission electron microscope as a function of the objective lens potential. In the course of this in situ calibration it was not necessary to disassemble the microscope or interrupt its operation. The procedure used is versatile and accurate enough to measure magnetic fields up to 20 kOe (mu(0)H=2 T in SI units) as was confirmed by subsequent Hall-probe field measurement of the same electron microscope. The calibration method described in this article does not require any special Hall-probe holder adaptations and can be applied to any transmission electron microscope or similar instrument. To illustrate the utility of the technique and its results, quantitative analysis of magnetic domain images obtained with Lorentz microscopy during magnetic reversal of a sample subjected to an in situ magnetic field in the JEM3000F microscope is presented and discussed. (C) 2002 American Institute of Physics.