Highly Sensitive Precise Double AC Hall Effect Apparatus for Wide Resistance Range

A double AC apparatus having new functions is described. So far, in a highly sensitive double AC apparatus, the false signal generation due to nonlinearity at terminal junctions of the specimen and induced emf has been a decisive drawback. In the present apparatus, which eliminates the induced emf in situ by using specially designed transformers, the false signal can be completely removed. This result enables us to measure, with high precision, the Hall emf down to a voltage level comparable to the thermal noise of the specimen. In addition, the current shunting effect by capacitances in the region of high specimen resistance is reduced by the proper arrangement of lead wire and by the bootstrapping technique. The upper limit of specimen resistance for which the Hall effect is measurable with the double AC method is extended up to 100 G Ω.