We report on extensive studies on the intrinsic sensitivity of a combined ³He/Cs magnetometer. The magnetometer relies on the detection of the free spin precession of nuclear spin polarized ³He by optically pumped cesium magnetometers. We characterize the relevant processes involved in the detection and quantify their impact on the total sensitivity of the magnetometer. An expression is derived that predicts the sensitivity of this magnetometer scheme and the results are compared to experiments. Excellent agreement is found between theory and experiments, and implications for an application of a ³He/Cs magnetometer in an experiment searching for a permanent neutron electric dipole moment are discussed
