NSF Nanosystems Engineering Research Center for Translational Applications of Nanoscale Multiferroic Systems TANMS

The coexistence of magnetism and ferroelectricity (FE) in the same crystalline phase of the so-called multiferroic (MF) material offers the opportunity of magnetoelectric (ME) coupling, which can lead to magnetization switching by an electric field or polarization switching by a magnetic field. Since this phenomenon allows the storage of information in nanometer-sized memories with four logic states, the issues of MFs are of prime interest. In the single-phase MFs, however, the electric polarization and magnetization interact weakly with each other while FM disappears far below room temperature. A more robust scenario of magnetoelectricity at room temperature occurs in artificial MFs composites consisting of FM thin films which are grown epitaxially on a ferroelectric substrate, shown in Fig. 1. In ME composites, neither of the constituent phases has ME effect, but the interaction between the phases across the interface can produce remarkable ME effect. Thus, MF superlattices offer the unique opportunity to combine different phases at the atomic level, where via precise control of the lattice mismatch, one can design novel interfacial ME structures. Depending on the particular FM and FE constituents there are two types of ME phenomena: (1) those which are mediated by elastic strain of the FE component and magnetostriction of the FM component; and (2) those where the ME effect is entirely controlled by electronic mechanism, such as electron screening and interface bonding. We propose to develop and apply sequential multiscale approaches linking (1) ab-initio based effective Hamiltonian and Monte Carlo approaches, (2) ab-initio based Landau-Lifshitz-Gilbert approaches, (3) ab initio and tight-binding calculations of spin transport and (4) phenomenological approaches to investigate: 1. MF superlattices based on a combination of different FM and FE materials 2. The effect of interfacial disorder on the ME coupling. 3. The electric field control of magnetocrystalline anisotropy 4. The strain-mediated control of ME coupling 5. Transport properties (tunnel magneto-resistance and spin torque) in FM/FE/FM tunnel junctions 6. The temperature-dependent transport in MF composites