DC and AC Characterization of MgO Magnetic Tunnel Junction Sensors

We have fabricated multiple MgO magnetic tunnel junctions (MTJ) with 1.7 nm oxide, which are connected in series, and layed out in a serpentine geometry. We performed DC tunnel magnetoresistance measurements and AC impedance spectroscopy with crossed DC magnetic fields in the easy and hard axis directions. A simple RLC circuit model is used to fit our data and characterize the dependence on capacitance (C) and inductance (L) of magnetization orientation of the MTJ sensors. We have found in our samples that C and L are higher in antiparallel than in parallel configuration. We discuss possible reasons for the existence of this field dependence and show the evolution of magnetic field vs. capacitance curve from memory mode into sensing mode at high frequencies.