Magnetic anisotropy by Rashba spin-orbit coupling in antiferromagnetic thin films

Magnetic anisotropy in an antiferromagnet (AFM) with inversion symmetry breaking (ISB) is investigated. The magnetic anisotropy energy (MAE) resulting from the Rashba spin-orbit and s-d type exchange interactions is determined for two different models of AFMs. The global ISB model, representing the effect of a surface, an interface, or a gating electric field, results in an easy-plane magnetic anisotropy. In contrast, for a local ISB model, i.e., for a noncentrosymmetric AFM, perpendicular magnetic anisotropy (PMA) arises. Both results differ from the ferromagnetic case, in which the result for PMA depends on the band structure and dimensionality. These MAE contributions play a key role in determining the direction of the Neel order parameter in antiferromagnetic nanostructures, and reflect the possibility of electrical-field control of the Neel vector.Comment: 4 pages, 2 figure

Spin-state transition and phase separation in multi-orbital Hubbard model

We study spin-state transition and phase separation involving this transition based on the milti-orbital Hubbard model. Multiple spin states are realized by changing the energy separation between the two orbitals and the on-site Hund coupling. By utilizing the variational Monte-Carlo simulation, we analyze the electronic and magnetic structures in hole doped and undoped states. Electronic phase separation occurs between the low-spin band insulating state and the high-spin ferromagnetic metallic one. Difference of the band widths in the two orbitals is of prime importance for the spin-state transition and the phase separation.Comment: 5 pages, 5 figure

Gauge Coupling Unification in GUT with Anomalous U(1) Symmetry

We show that in the framework of grand unified theory (GUT) with anomalous $U(1)_A$ gauge symmetry, the success of the gauge coupling unification in the minimal SU(5) GUT is naturally explained, even if the mass spectrum of superheavy fields does not respect SU(5) symmetry. Because the unification scale for most realizations of the theory becomes smaller than the usual GUT scale, it suggests that the present level of experiments is close to that sufficient to observe proton decay via dimension 6 operators, $p\to e+\pi$.Comment: 4 pages, RevTeX, to appear in Phys.Rev.Let

Current-spin coupling for ferromagnetic domain walls in fine wires

The coupling between a current and a domain wall is examined. In the presence of a finite current and the absence of a potential which breaks the translational symmetry, there is a perfect transfer of angular momentum from the conduction electrons to the wall. As a result, the ground state is in uniform motion. This remains the case when relaxation is accounted for. This is described by, appropriately modified, Landau-Lifshitz-Gilbert equations.Comment: 4 pqges, no figure

Co-operative density wave and giant spin gap in the quarter-filled zigzag ladder

Strong co-operative interactions occur between four different broken symmetries involving charge-ordering and bond distortions in the quarter-filled correlated zigzag electron ladder. The ground state is singlet, with spin gap several times larger than in the spin-Peierls state of the one-dimensional quarter-filled chain with the same parameters. We propose the quarter-filled zigzag electron ladder model for several different organic charge-transfer solids with coupled pairs of quasi-one-dimensional stacks, the spin-gap transition temperatures in which are unusually high.Comment: 4 pages, 4 EPS figures. accepted in Physical Review Letter

Sliding Singlet Mechanism Revisited

We show that the unification of the doublet Higgs in the standard model (SM) and the Higgs to break the grand unified theory (GUT) group stabilizes the sliding singlet mechanism which can solve the doublet-triplet (DT) splitting problem. And we generalize this attractive mechanism to apply it to many unified scenarios. In this paper, we try to build various concrete E_6 unified models by using the generalized sliding singlet mechanism.Comment: 13 page

Ferromagnetic resonance with a magnetic Josephson junction

We show experimentally and theoretically that there is a coupling via the Aharonov-Bohm phase between the order parameter of a ferromagnet and a singlet, s-wave, Josephson supercurrent. We have investigated the possibility of measuring the dispersion of such spin waves by varying the magnetic field applied in the plane of the junction and demonstrated the electromagnetic nature of the coupling by the observation of magnetic resonance side-bands to microwave induced Shapiro steps.Comment: 6 pages, 5 figure

Field-induced Orbital Patterns in Ferromagnetic Layered Ruthenates

We study the evolution of orbital patterns in ferromagnetic layered ruthenates due to the competition of Coulomb interactions, compressive c axis and orthorhombic distortions in the presence of a polarizing orbital field coupled to the angular momentum. By means of the exact diagonalization on a 2x2 cluster and a cluster embedded analysis where inter-plaquette interaction is treated on mean field level, we determine the ground-state phase diagram. Specifically, we demonstrate that, via the activation of two or three of t_2g local orbital configurations, an external field applied along different symmetry directions can lead to inequivalent orbital correlated states. Starting from an antiferro-orbital pattern, for the easy axis case an orbital ordered phase is induced, having strong next nearest neighbors ferro-orbital correlations. Otherwise, a field applied along the hard axis leads a reduction of local orbital moment in a way to suppress the orbital order.Comment: 11 page