Miniature atomic magnetometer integrated with flux concentrators

High permeability magnetic flux concentrators are used to enhance the sensitivity of an atomic magnetometer operating in the spin-exchange relaxation-free regime. The magnetometer uses a millimeter scale (87)Rb vapor cell and either mu-metal or Mn-Zn ferrite flux concentrators. The measured sensitivity gives excellent agreement with calculations of thermal noise from the concentrator material. The mu-metal concentrators allow a sensitivity of 50 fT Hz(-1/2), limited by thermal current magnetic noise. The ferrite concentrators are limited by thermal magnetization noise at low frequencies, and reach a sensitivity of 10 fT Hz(-1/2) for frequencies above 125 Hz.