An unexplored physical mechanism which produces a magnetoelectric effect in ferroelectric-ferromagnetic multilayers is studied based on first-principles calculations. Its origin is a change in bonding at the ferroelectric-ferromagnet interface that alters the interface magnetization when the electric polarization reverses. Using Fe/BaTiO3 multilayers as a representative model, we show a sizable difference in magnetic moments of Fe and Ti atoms at the two interfaces dissimilar by the orientation of the local electric dipole moments. The predicted magnetoelectric effect opens a new direction to control magnetic properties of thin-film layered structures by electric fields.

† Co-first authors Magnetic tunnel junctions (MTJs), composed of two ferromagnetic electrodes separated by a thin insulating barrier layer, are currently used in spintronic devices, such as magnetic sensors and magnetic random access memories. Recently, driven by demonstrations of ferroelectricity at the nanoscale, thin-film ferroelectric barriers were proposed to extend the functionality of MTJs. Due to the sensitivity of conductance to the magnetization alignment of the electrodes (tunnelling magnetoresistance) and the polarization orientation in the ferroelectric barrier (tunnelling electroresistance), these multiferroic tunnel junctions (MFTJs) may serve as four-state resistance devices. Based on first-principles calculations we demonstrate four resistance states in SrRuO 3 /BaTiO 3 /SrRuO 3 MFTJs with asymmetric interfaces. We find that the resistance of such a MFTJ is significantly changed when the electric polarization of the barrier is reversed and/or when the magnetizations of the electrodes are switched from parallel to antiparallel. These results reveal the exciting prospects of MFTJs for application as multifunctional spintronic devices.The field of spintronics has been successful in producing magnetoresistive devices for magnetic memory and sensor applications.

We discuss the electronic structure, lattice dynamics and electron-phonon interaction of newly discovered superconductor LaO0.5F0.5BiS2 using density functional based calculations. A strong Fermi surface nesting at k=(π,π,0) suggests a proximity to charge density wave instability and leads to imaginary harmonic phonons at this k point associated with in-plane displacements of S atoms. Total energy analysis resolves only a shallow double-well potential well preventing the appearance of static long-range order. Both harmonic and anharmonic contributions to electronphonon coupling are evaluated and give a total coupling constant λ ≃ 0.85 prompting this material to be a conventional superconductor contrary to structurally similar FeAs materials. Here, the basic structural unit is the BiS 2 layer which is similar to the Cu-O planes in Cu-based superconductors[1] and the Fe-A (A=P, As, Se, Te) planes in iron pnictides [5]. A chance to explore superconductivity and increase T c in these new compounds has already resulted in a lot of work that appeared shortly after the discovery [1,7,[9][10][11][12][13][14][15][16]. Hall effect measurements reveal multiband features and suggest the superconducting pairing occurs in one-dimensional chains [10]. It was proposed that these compounds are type II superconductors and good candidates for thermoelectric materials [11]. Electrical resistivity measurements under pressure reveal that Bi 4 O 4 S 3 and La(O,F)BiS 2 have different T c versus pressure behavior, and the Fermi surface of La(O,F)BiS 2 may be located in the vicinity of some instabilities [12]. A two p bands electronic model has been proposed based on band structure calculation [13], and a