The spin dependence of the lifetime of electrons excited in ferromagnetic cobalt is measured directly in a femtosecond real-time experiment. Using time-and spin-resolved two photon photoemission, we show that the lifetime of majority-spin electrons at 1 eV above the Fermi energy is twice as long as that of minority-spin electrons. The results demonstrate the feasibility of studying spin-dependent electron relaxation in ferromagnetic solids directly in the time domain and provide a basis for understanding the dynamics of electron transport in ferromagnetic solids and thin films. [S0031-9007(97)04853-9]

Based on a general discussion of orthogonalization effects, two new one-electron orthogonalization corrections are derived to improve existing semiempirical models at the neglect of diatomic differential overlap level. The first one accounts for valence-shell orthogonalization effects on the resonance integrals, while the second one includes the dominant repulsive core–valence interactions through an effective core potential. The corrections for the resonance integrals consist of three-center terms which incorporate stereodiscriminating properties into the two-center matrix elements of the core Hamiltonian. They provide a better description of conformational properties, which is rationalized qualitatively and demonstrated through numerical calculations on small model systems. The proposed corrections are part of a new general-purpose semiempirical method which will be described elsewhere

Semiempirical orthogonalization-corrected methods (OM1, OM2, and OM3) go beyond the standard MNDO model by explicitly including additional interactions into the Fock matrix in an approximate manner (Pauli repulsion, penetration effects, and core–valence interactions), which yields systematic improvements both for ground-state and excited-state properties. In this Article, we describe the underlying theoretical formalism of the OMx methods and their implementation in full detail, and we report all relevant OMx parameters for hydrogen, carbon, nitrogen, oxygen, and fluorine. For a standard set of mostly organic molecules commonly used in semiempirical method development, the OMx results are found to be superior to those from standard MNDO-type methods. Parametrized Grimme-type dispersion corrections can be added to OM2 and OM3 energies to provide a realistic treatment of noncovalent interaction energies, as demonstrated for the complexes in the S22 and S66×8 test sets.

Ultrafast magnetic field pulses as short as 2 picoseconds are able to reverse the magnetization in thin, in-plane, magnetized cobalt films. The field pulses are applied in the plane of the film, and their direction encompasses all angles with the magnetization. At a right angle to the magnetization, maximum torque is exerted on the spins. In this geometry, a precessional magnetization reversal can be triggered by fields as small as 184 kiloamperes per meter. Applications in future ultrafast magnetic recording schemes can be foreseen.

Molecular semiconductors may exhibit antiferromagnetic correlations well below room temperature. Although inorganic antiferromagnetic layers may exchange bias single-molecule magnets, the reciprocal effect of an antiferromagnetic molecular layer magnetically pinning an inorganic ferromagnetic layer through exchange bias has so far not been observed. We report on the magnetic interplay, extending beyond the interface, between a cobalt ferromagnetic layer and a paramagnetic organic manganese phthalocyanine (MnPc) layer. These ferromagnetic/organic interfaces are called spinterfaces because spin polarization arises on them. The robust magnetism of the Co/MnPc spinterface stabilizes antiferromagnetic ordering at room temperature within subsequent MnPc monolayers away from the interface. The inferred magnetic coupling strength is much larger than that found in similar bulk, thin or ultrathin systems. In addition, at lower temperature, the antiferromagnetic MnPc layer induces an exchange bias on the Co film, which is magnetically pinned. These findings create new routes towards designing organic spintronic devices.