Ultrahigh sensitivity magnetic field and magnetization measurements with an atomic magnetometer

We describe an ultrasensitive atomic magnetometer based on optically pumped potassium atoms operating in a spin-exchange relaxation free regime. We demonstrate magnetic field sensitivity of 160 aT/Hz(1/2) in a gradiometer arrangement with a measurement volume of 0.45 cm(3) and energy resolution per unit bandwidth of 44h. As an example of an application enabled by such a magnetometer, we describe measurements of weak remnant rock magnetization as a function of temperature with a sensitivity on the order of 10(-10) emu/cm(3)/Hz(1/2) and temperatures up to 420 degrees C. (C) 2010 American Institute of Physics. [doi:10.1063/1.3491215]