Conductance, magnetoresistance, and interlayer exchange coupling in magnetic tunnel junctions with nonmagnetic metallic spacers and finite thick ferromagnetic layers

Abstract

Based on the two-band model and free-electron approximation, magnetism and transport properties of magnetic tunnel junctions with nonmagnetic metallic (NM) spacers and finite thick ferromagnetic (FM) layers are studied. The mean conductance and tunnel magnetoresistance are oscillatory functions of NM and FM thicknesses, their period is determined by the Fermi-surface properties of the metals, and magnetoresistances $(\ensuremath{\sim}{10}^{3}%)$ much greater than those predicted by Julliere's model are obtained. The oscillation of interlayer exchange coupling with metal layer thickness that originates from the interference of electron waves at different energy levels is found in contrast with the situation in metallic magnetic multilayers. Our results indicate that giant tunnel magnetoresistances with weak antiferromagnetic coupling can be attained by controlling the metal layer thickness, and this has potential in designing spin-polarized tunneling devices.