The effect of interlayers on magnetoresistance and exchange coupling in magnetic tunnel junctions

Based on a two-band model, we investigated the interlayer effect on the tunnel magnetoresistance (TMR) and the bilinear exchange coupling in a structure of Ferromagnet/Interlayer/Insulator/Ferromagnet [FM/Interlayer/I/FM] tunnel junction with nonmagnetic (NM) metal layer on both sides. We found that the TMR and the exchange coupling can be greatly modified by introducing an FM or NM interlayer into the basic FM/I/FM structure. The TMR ratio and the exchange coupling oscillated with the thickness of the interlayer. However, the oscillation period in the cases of FM and NM interlayer is different, suggesting a more sensitive dependence of the spin electronic density of states on an NM interlayer. The change of the TMR and the bilinear exchange coupling has the same period and phase for the same type of interlayer. The bilinear exchange coupling decreases exponentially with the increase of the barrier thickness. The sign and the strength of the exchange coupling in NM/FM/Interlayer/I/FM/NM structure can been well controlled by changing the thickness of NM or FM interlayer, suggesting another way to control the exchange coupling in spin-polarized tunneling devices.