Hall effect materials ( Bismuth and Germanium) are available. A hall effect probe (in the form of the MBL Force Probe) is also available. With this probe connected to the computer you can plot the strength of a magnetic field. Sensitive enough to show the earth's magnetic field and demonstrate the field is uniform between a set of Helmholts Coils. A Thorton hall probe connected to a microvolt amplifier output connected to a voltmeter is also available.