Loss of spin polarization of tunnelling currents due to electrostatic screening at magnetoresistive ferromagnet/ferroelectric tunnel junctions

Magnetoelectric coupling inherent to the bulk of multiferroic films or control of spin orientation in magnetic layers via piezoelectric strain in composite layers have been two forthcoming approaches to enable electric control of magnetic order. Spin-dependent screening occuring at dielectric/ferromagnet interfaces is another magnetoelectric effect important for spin selective tunnel junctions. Here, we analyze the spin-dependent screening of ferroelectric polarization in a film interfacing ferromagnetic electrodes using the continuity equations. We show that local spin population (LSP) in spin subbands near the interfaces can dramatically deviate from bulk, which is in qualitative agreement with recent first principles results. We compute the tunneling currents for majority and minority spins using the Wentzel-Kramers-Brillouin approximation and demonstrate that spin polarization tends to disappear for increasing values of ferroelectric polarization in direct connection with the increase in subband LSP for minority spins. We argue that the reduction in TMR due to spin mixing at the interfaces will be much more prominent in comparison to defect scattering and magnon-driven losses in spin polarization.