Loss of spin polarization in ferromagnet/ferroelectric tunnel junctions due to screening effects

Abstract

Electric field control of magnetization allows further miniaturization of integrated circuits for binary bit processing and data storage as it eliminates the need for bulky sophisticated systems to induce magnetic fields. Magnetoelectric coupling inherent to the bulk of multiferroic films or control of spin orientation in magnetic layers via piezoelectric strain in dual component composites have been two approaches standing out. Another magnetoelectric effect is spin-dependent screening that occurs at dielectric/ferromagnet interfaces which is of great importance 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 in continuum media. The competition between the electrostatic and the magnetochemical potential in the FM electrodes gives rise to a reduction in the net magnetic moment near the interface due to spin mixing, extending to a distance comparable to the Thomas-Fermi screening length. Our continuum media treatment shows that the local spin population 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 the majority and minority spins using the Wentzel-Kramers-Brillouin approximation as a function of ferroelectric polarization. We find that the spin polarization tends to disappear for increasing values of ferroelectric polarization in direct connection with the increase in subband spin population for minority spins at the interface.

Existence of two spin dynamics in the temperature and magnetic field dependence of the magnetization curves of ferrimagnetic Co1.75Fe1.25O4 and its composite with BaTiO3

“…This is evidenced from the increase of ferrimagnetic softness in composite sample. There is a possibility of magneto-electric coupling at the interfaces of CF80 and BTO particles [16][17] or a hidden interface driven exchange coupling in oxide heterostructures [31].…”

“…It is characterized by ageing effects. The training effect, on the other hand, originates from an irreversible change in the pinned spin structure at domain walls or at the interfaces of FM-AFM structure of materials or at the interfaces of ferromagnetic and ferroelectric systems [9,[16][17].…”

Spin-polarized currents driven by spin-dependent surface screening

“…It has been shown experimentally that SS may be utilized to change the magnetization, anisotropy or coercivity of ultrathin ferromagnetic film [7][8][9][10][11][12][13][14], to induce magnetic ordering transition [15,16] or even induce surface magnetism in nonmagnetic materials [17]. In multiferroic tunnel junctions SS provides significant contribution to the tunneling resistance [18,19] and opens possibilities to manipulate the spin polarization of tunneling electrons [20,21]. Owing to the surface magnetic anisotropy that is controlled by SS, spin waves may be excited parametrically or resonantly with the ac voltage [22][23][24][25][26].…”