Low magnetic field measurement with a reversed-field electron-spin-resonance magnetometer

An effective method of measuring low magnetic fields is presented. In this method, the magnetic field direction is reversed periodically so that the effects of external magnetic fields, such as the earth's magnetism, are removed. The usefulness of the method is investigated by using a split coil magnetic field source and an electron-spin-resonance magnetometer. A magnetic field of 10 mT can be measured with an uncertainty of less than 0.2 /spl mu/T, i.e., 20 ppm.