A multiferroic tunnel junction (MFTJ) basically consists of a thin ferroelectric (FE) layer sandwiched between two ferromagnetic (FM) electrodes, with the FE and FM modes coupled to form a four states magnetoelectric device. The interaction between the FE barrier and the FM electrodes in a MFTJ allows a multitude of possibilities for applications including but not limited to (multiple state) ferroelectric memories, quantum tunneling junctions, photoferroic solar cells, multiple resistive junctions, etc..

The conductance of a MFTJ depends on both the polarization switching of the FE barrier (tunneling electroresistance, TER) and the relative directions of magnetization in the FM electrodes (tunneling magnetoresistance, TMR). The stability of the FE polarization, the magnitude and anisotropy of magnetization, the strength of their coupling, as well as the TER and TMR are important design parameters of MFTJs. In this Project, using first principles calculations and methods based on partial differential equations, covering three orders of magnitude length scale (0.1-100 nm), we aim at new designs of MFTJs with pre-determined functionalities for next generation charge and spin electronics. The key property for device functionality is the polarization dependent change of the energy band alignment at the electrode-ferroelectric interface.

Since in real implementations the interface properties (strains, chemistry, defect state, charge acummulations, potential profile) have a critical effect on the band alignment and therefore on the electrical performance of the junction, a special attention is given to engineering the FE-FM interface properties.

Conceptual schemes of the magnetic tunnel junction (MTJ), a); ferroelectric tunnel junction (FTJ), b); and multiferroic tunnel junction (MFTJ), c). The conductance of a MFTJ depends on both the polarization switching of the FE barrier (tunneling electroresistance, TER) and the relative directions of magnetization in the FM electrodes (tunneling magnetoresistance, TMR).

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