  A practical problem for memory applications involving perpendicularly
magnetized magnetic tunnel junctions is the reliability of switching
characteristics at high-bias voltage. Often it has been observed that at
high-bias, additional error processes are present that cause a decrease in
switching probability upon further increase of bias voltage. We identify the
main cause of such error-rise process through examination of switching
statistics as a function of bias voltage and applied field, and the junction
switching dynamics in real time. These experiments show a coincidental onset of
error-rise and the presence of a new low-frequency microwave emission well
below that dictated by the anisotropy field. We show that in a few-macrospin
coupled numerical model, this is consistent with an interface region with
concentrated perpendicular anisotropy, and where the magnetic moment has
limited exchange coupling to the rest of the layers. These results point to the
important role high-frequency interface magnetic moment dynamics play in
determining the switching characteristics of these tunnel junction devices.
