The magnetization and magnetic anisotropy of FeCo/MgO(001) thin film under electric field were investigated by the first-principles calculations. Three different interface configurations were considered: Co/Fe/MgO, Fe/Co/MgO, and FeCo/FeCo/MgO. It was found that the perpendicular anisotropy was preferred for all the configurations and enhanced with increasing electric field, which was consistent with experimental results. Furthermore, our calculations indicated that the FeCo/FeCo/MgO was the most stable configuration and had the largest perpendicular magnetic anisotropy energy. The results also showed that the FeCo/FeCo/MgO and Fe/Co/MgO configurations had larger magnetoelectric coefficients than those of the Co/Fe/MgO configuration and previous report about the Fe/MgO interface.

We present a stoichiometry-dependent structural phase transition in SrRuO3 film on SrTiO3 substrate. The oxygen stoichiometry in the films was varied by changing the oxygen partial pressure P(O2) during the deposition process. For SrRuO3 films with P(O2) ≥ 60 mTorr, they exhibited a pseudo-orthorhombic structure with in-plane uniaxial magnetic anisotropy. On the other hand for films with P(O2) ≤ 45 mTorr, the tetragonal SrRuO3 phase with a perpendicular uniaxial magnetic anisotropy was stabilized at room temperature. The big difference in the magnetic anisotropy of these two SrRuO3 phases was shown to be closely linked to their respective RuO6 octahedral rotation patterns: the RuO6 octahedra rotate differently along the two orthogonal in-plane directions in the pseudo-orthorhombic phase, whereas in the tetragonal phase only octahedral rotations around z-axis are present and the octahedral tilts along the in-plane axes are diminished. First-principles calculations show that such a suppression of the RuO6 octahedra tilting in the tetragonal phase arises from the oxygen vacancies at the octahedral apex (along z-axis). This work demonstrates that the stoichiometry plays an important role in determining the octahedral rotations and tilts in the perovskite materials, which may induce new phases with distinctively different structural symmetry and physical property.

Recent experiments and computer simulation studies on nano-confined ionic liquids(ILs) has shifted the focus from perpendicular to lateral distribution, the understanding of which is crucial for ILs performance in the field of energy storage system and tribology. In this article, the structure of 1-ethyl-3-methylimidazolium Bromide, [Emim][Br], confined by hydroxyl group functionalized surface of kaolinite plates has been studied by molecular dynamics simulation. Depending on the degree of confinement, ILs anion can pack into a 2D ordered structure with square symmetry, coexisted liquid/solid phase or liquid-like structure. The ordered structure arises from surface-induced ionic orientational preference and the driving force from confinement that supports the formation of 2D planar structure. The flexible H-bond formed between Br and surface hydroxyl group at fixed d-spacing results in the liquid-like ordering that breaks down the electrostatic network in ILs. The influence of water addition varies when confining plates are treated differently, namely forming large H-bonding network and small isolated oligomers, for relaxed and fixed d-spacing, respectively. This work reveals additional information about the relative importance of factors like packing constrains, interaction within ILs and selective attraction in determining the structure and dynamics of confined ILs.

The magnetic anisotropy of the FeCo/MgO(001) thin films with the effects of thickness, the electric field, and the strain of the in-plane lattice constant were investigated by first-principles calculations. The thickness dependence of the magnetic anisotropy of FeCo ultrathin films in the range of one to four monolayers was explored, and the films with one, three, and four FeCo monolayers preferred the in-plane easy axis of magnetization, while the film with two FeCo monolayers occupied the perpendicular anisotropy. In the presence of an electric field, the magnetic anisotropy energies for all four films could be enhanced; moreover, the transition of the easy axis of magnetization from in-plane to out-of-plane also could be obtained, and the transition electric field was related with their thickness. It could be found that the variation of the in-plane lattice constant resulted in the switching from the perpendicular to in-plane anisotropy for the film with two FeCo monolayers.

Epitaxial SrRuO3 films were grown under different oxygen partial pressures inducing different amounts of oxygen vacancies. In spite of microstructural disorders, a considerable improvement in the conductivity was observed at ambient temperature with increasing the oxygen vacancies. The oxygen vacancies are responsible for the conductivity improvement by enhancing the orbital overlap between Ru dz2 and O pz orbitals. The finding indicates that the oxygen vacancy plays an important role in determining the transport properties of perovskite oxides, by modifying their electronic structures.

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The effects of the spin transition on the electronic structure, thermal expansivity and lattice thermal conductivity of ferropericlase are studied by first principles calculations at high pressures. The electronic structures indicate that ferropericlase is an insulator for high-spin and low-spin states. Combined with the quasiharmonic approximation, our calculations show that the thermal expansivity is larger in the high-spin state than in the low-spin state at ambient pressure, while the magnitude exhibits a crossover between high-spin and low-spin with increasing pressure. The calculated lattice thermal conductivity exhibits a drastic reduction upon the inclusion of ferrous iron, which is consistent with previous experimental studies. However, a subsequent enhancement in the thermal conductivity is obtained, which is associated with the spin transition. Mechanisms are discussed for the variation in thermal conductivity by the inclusion of ferrous iron and the spin transition.