We develop a plane-wave pseudopotential scheme for noncollinear magnetic structures, based on a generalized local spin-density theory in which the direction of the magnetization is a continuous variable of position. We allow the atomic and magnetic structures to relax simultaneously and selfconsistently. Application to small Fe clusters yields noncollinear magnetic structures for Fe 3 and Fe 5 . The components of the magnetization density vary smoothly with position. The spin direction undergoes sizable changes only in the regions of small charge and spin density between the atoms and is generally uniform in the magnetic regions of the atoms. [S0031-9007(98)05870-0] PACS numbers: 71.15.Pd, 71.24. + q, 75.50.Bb Most local spin-density calculations assumed so far complete spin alignment throughout the system, resulting in collinear magnetic structures. This approach is suitable for describing ferromagnetic or antiferromagnetic order, usually encountered in crystals. There are, however, cases where noncollinear spin arrangements may occur, such as, e.g., in the g phase of Fe which exhibits a spin-spiral structure [1,2]. More generally, noncollinear configurations occur more easily in magnetic systems in a low symmetry or in a disordered state [3,4]. Furthermore, noncollinearity is crucial for dealing with magnetic excitations, such as spin waves, or to treat magnetism at finite temperature [5][6][7].A number of generalized spin-density calculations allowing for noncollinear structures have been performed [2,5,[6][7][8][9][10][11][12]. All of these calculations adopted the atomic sphere approximation for the crystal potential and assumed a uniform spin direction within each atomic sphere. Although the latter approximation seems well justified from a physical point of view, the actual spatial variation of spin directions as it would result from a fully unconstrained calculation is not known. In addition, the atomic sphere approximation is not reliable for atomic relaxations and, as a consequence, its application is restricted to cases in which the atomic geometry is a priori known.To address the above issues, we adopt a scheme based on pseudopotentials and plane waves in which both the direction and the magnitude of the magnetization are fully unconstrained as a function of position. This approach combines noncollinear local spin-density calculations with the ab initio molecular dynamics method [13], which deals efficiently with the simultaneous relaxation of electronic and ionic degrees of freedom. We apply our scheme to small Fe clusters and find that some geometrical structures are characterized by noncollinear spin arrangements, which appear to be favored by an increase of the atomic spin moments. In particular, the ground state of Fe 5 is found to be noncollinear. The noncollinear structures that we find allow us to study how the spins change their orientation as a function of position and to check the validity of the common assumption of uniform spin direction within the atomic regions.In generalized local ...

We have investigated crystalline magnetic anisotropy in the electric field (EF) for the Fe-Pt surface which have a large perpendicular anisotropy, by means of the first-principles approach.The anisotropy is reduced linearly with respect to the inward EF, associated with the induced spin density around the Fe layer. Although the magnetic anisotropy energy (MAE) density reveals the large variation around the atoms, the intrinsic contribution to the MAE is found to mainly come from the Fe layer.

Primary and secondary streamers of positive pulsed corona discharge are observed in a point-to-plane gap using a short-gated intensified CCD camera in an air-like environment. The influences of oxygen concentration and applied voltage on the properties of both streamers are presented. It is shown that the propagation velocity, the diameter, and the shape of the streamers are strongly influenced by the oxygen concentration. In pure nitrogen, the primary streamer shows branching with a diameter of about 0.2-0.4 mm, while in air, the branching disappears almost completely and the shape of the primary streamer becomes quite smooth with a diameter of more than 1 mm. After the arrival of the primary streamer at the cathode, a secondary streamer develops from the anode toward the cathode as far as the middle of the gap. The propagation length of the secondary streamer increases approximately linearly with the applied voltage. It is shown that the ratio of the energy consumed by the secondary streamer to the whole energy consumed by the discharge increases with the applied voltage.

The polarization vector of the Rashba spin, which must be parallel to the two-dimensional (2D) plane in an ideal system, is found to change abruptly and definitely to the direction perpendicular to the surface at the K̅ point of the Brillouin zone of a real hexagonal system, the Tl/Si(111)-(1×1) surface. This finding obtained experimentally by angle-resolved and spin-resolved photoemission measurements is fully confirmed by a first-principles theoretical calculation. We found that the abrupt rotation of the Rashba spin is simply understood by the 2D symmetry of the hexagonal structure

The gas temperature and OH density in the afterglow of pulsed positive corona discharge are measured using the laser-induced predissociation fluorescence (LIPF) of OH radicals. Discharge occurs in a 13 mm point-to-plane gap in an atmospheric-pressure H2O(2.8%)/O2(2.0%)/N2 mixture. The temperature measurement shows that (i) the temperature increases after discharge and (ii) the temperature near the anode tip (within 1 mm from the anode tip) is much higher than that of the rest of the discharge volume. Near the anode tip, the temperature increases from 500 K (t = 0 µs) to 1100 K (t = 20 µs), where t is the postdischarge time, while it increases from 400 K (t = 0 µs) to 700 K (t = 100 µs) in the rest of the discharge volume away from the anode tip. This temperature difference between the two volumes (near and far from the anode tip) causes a difference in the decay rate of OH density: OH density near the anode tip decays approximately 10 times slower than that far from the tip. The spatial distribution of OH density shows good agreement with that of the secondary streamer luminous intensity. This shows that OH radicals are mainly produced in the secondary streamer, not in the primary one.