Using small, rare‐earth magnets to study the susceptibility of feebly magnetic metals

Small rare‐earth magnets have remarkable properties that can be exploited in the construction of simple measuring devices. Examples are a torsion pendulum that measures the earth’s horizontal magnetic field and a gravimetric pendulum that responds to the small susceptibilities of various ‘‘nonmagnetic’’ materials. These preliminary demonstrations lead to the design of a practical device for measuring the susceptibilities of feebly magnetic metals in low magnetic fields. Our laboratory has used this last method to determine relatively small magnetic susceptibilities, down to 0.0003, to an uncertainty of less than 20%. A convenient feature of our apparatus is that calibration by a susceptibility standard is not required.