Faraday Balance for Measuring Magnetic Susceptibility

Abstract

An apparatus for measuring magnetic susceptibility by the Faraday method is described. It is capable of measuring susceptibilities ranging from 0.01×10−6 to 500×10−6 emu/g over a temperature range of 5 to 300 K, in fields up to 10 kOe, with a precision of 0.2% and an accuracy of 1%. Various problems associated with the measurements, such as thermomolecular flow, ferromagnetic impurities, and electrostatic forces, are discussed It is shown that problems arising from thermomolecular flow can be avoided by controlling the pressure of exchange gas. Correction for ferromagnetic impurities involves extrapolating the susceptibility vs 1/H to infinite field. Several methods for minimizing the problems caused by electrostatic force are discussed. The versatility of the balance is demonstrated by measurements made on NiTiO3 (χmax=229×10−6 emu/g) and K0.3 MoO3 (χ≈0.06×10−6 emu/g).