Interface effects at a half-metal/ferroelectric junction

Magnetoelectric effects are investigated ab-initio at the interface between half-metallic and ferroelectric prototypes: Heusler Co$_2$MnSi and perovskite BaTiO$_3$. For the Co-termination ferroelectricity develops in BaTiO$_3$ down to nanometer thicknesses, whereas for the MnSi-termination a paraelectric and a ferroelectric state energetically compete, calling for a full experimental control over the junction atomic configuration whenever a ferroelectric barrier is needed. Switch of the electric polarization largely affects magnetism in Co$_2$MnSi, with magnetoelectric coupling due to electronic hybridization at the MnSi termination and to structural effects at the Co-termination. Half-metallicity is lost at the interface, but recovered already in the subsurface layer.Comment: 4 pages, 3figures, accepted for publication in Appl. Phys. Let

Charge-induced spin polarization in non-magnetic organic molecule Alq3_{3}

Electrical injection in organic semiconductors is a key prerequisite for the realization of organic spintronics. Using density-functional theory calculations we report the effect of electron transfer into the organic molecule Alq$_3$. Our first-principles simulations show that electron injection spontaneously spin-polarizes non-magnetic Alq$_3$ with a magnetic moment linearly increasing with induced charge. An asymmetry of the Al--N bond lengths leads to an asymmetric distribution of injected charge over the molecule. The spin-polarization arises from a filling of dominantly the nitrogen $p_z$ orbitals in the molecule's LUMO together with ferromagnetic coupling of the spins on the quinoline rings.Comment: Accepted 4 pages 4 figure

Magnetization dynamics in disordered Fex_xCo1−x_{1-x} alloys : A first-principles augmented space approach and atomistic spin dynamics simulations

In this paper, we present a general method to study magnetization dynamics in chemically disordered alloys. This computationally feasible technique, which seamlessly combines three approaches : the density functional based linear muffin-tin orbitals (LMTO) for self-consistently obtaining a sparse Hamiltonian; the generalized recursion method to obtain the one and two-particle Green functions and augmented space approach to deal with disorder averaging. The same formalism applied to both spectral and response properties should make the errors compatible in different studies. %The underlying computational routines are optimized and parallelized for ease of handling. We have demonstrated a successful application to the binary chemically disordered Fe$_x$Co$_{1-x}$ alloys to explain several experimental features in magnon spectra. Our study captures significant magnon softening due to magnon-electron scattering for chemically disordered Fe$_x$Co$_{1-x}$ alloys within linear spin wave regime. As a complementary study, we have done atomistic spin dynamics simulations by solving Landau-Lifshitz-Gilbert equation with parameters obtained from ab initio multiple scattering theory to compare with the results obtained from augmented space approach.Comment: arXiv admin note: text overlap with arXiv:1102.4551, arXiv:1304.7091 by other author

Exchange parameters and adiabatic magnon energies from spin-spiral calculations

We present a method of extracting the exchange parameters of the classical Heisenberg model from first-principles calculations of spin-spiral total energies based on density functional theory. The exchange parameters of the transition-metal monoxides MnO and NiO are calculated and used to estimate magnetic properties such as transition temperatures and magnon energies. Furthermore we show how to relate the magnon energies directly to differences in spin-spiral total energies for systems containing an arbitrary number of magnetic sublattices. This provides a comparison between magnon energies using a finite number of exchange parameters and the infinite limit