We have studied the low frequency complex magnetization dynamics in Co/Al_2O_3/Ni_80Fe_20 magnetic tunnel junctions (MTJs) at temperatures between 4.2 K and 300K.The measurements were carried out by using two different experimental techniques.The first method probes directly magnetic properties via DC magnetization and AC susceptibility,while the second one measures AC magnetization dynamics for the ferromagnetic electrodes near the cross area,which is related to the tunneling resistance.
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