Alternate Current Apparatus for Measuring the Ordinary Hall Coefficient of Ferromagnetic Metals and Semiconductors

Abstract

An apparatus is described for measuring the ordinary Hall coefficient of ferromagnetic metals such as Ni and of ferrimagnetic semiconductors such as Fe3O4. An alternating electric field at 1000 cps is used with a static magnetic field. The apparatus has a sensitivity of 10−18 watt, a noise level of 10−9 volt, and a voltage resolution of one part in 105. The sensitivity is required by the small ordinary Hall coefficient of the metals and the ferrites, and the resolution is needed to separate the ordinary and extraordinary Hall effects. The apparatus may be used with sample impedances ranging from less than one ohm to several thousand ohms. The sample holders which are an important part of the apparatus are described. The measurement technique is detailed as is a method for ensuring the absence of spurious voltages. The system may also be used to measure changes in other second-order effects by bucking out all first-order effects.