Oscillatory behavior of tunnel magnetoresistance in a magnetic tunnel junction with varying magnetic layer thickness

Abstract

We theoretically study the dependence of the tunnel magnetoresistance (TMR) of an MgO-based magnetic tunnel junction (MTJ) on the thickness of the ferromagnetic (FM) layers. Our results show that the TMR ratio oscillates with the thickness of the FM layers. The amplitude of these oscillations is much greater than the one expected to occur in giant magnetoresistance devices. This is explained by the presence of the tunnel barrier, which reduces the number of propagating states, thus, limiting the effect of destructive interference and by the special nature of the � 1 band in Fe. Calculations taking interfacial roughness in the MTJ into account show that the oscillations are robust against disorder. They are expected to affect the TMR ratio of experimental MTJ where one of the ferromagnetic electrodes has a thickness less than the diffusion length. We speculate that small variations in the FM electrode thickness could be related to the observed, but so far unexplained, oscillations of TMR with MgO thickness.