Spin-torque ac impedance in magnetic tunnel junctions
  Subjecting a magnetic tunnel junction (MTJ) to a spin current and/or electric voltage induces magnetic precession, which can reciprocally pump current through the circuit. This results in an ac impedance, which is sensitive to the magnetic field applied to the MTJ. Measuring this impedance can be used to characterize the coupling between the magnetic free layer and the electric current as well as a read-out of the magnetic configuration of the MTJ. 
Silas Hoffman, Pramey Upadhyaya, Yaroslav Tserkovnyak
cond-mat.mes-hall