Domain wall propagation due to the synchronization with circularly polarized microwaves

Finding a new control parameter for magnetic domain wall (DW) motion in magnetic nanostructures is important in general and in particular for the spintronics applications. Here, we show that a circularly polarized magnetic field (CPMF) at GHz frequency (microwave) can efficiently drive a DW to propagate along a magnetic nanowire. Two motion modes are identified: rigid-DW propagation at low frequency and oscillatory propagation at high frequency. Moreover, DW motion under a CPMF is equivalent to the DW motion under a uniform spin current in the current perpendicular to the plane magnetic configuration proposed recently by Khvalkovskiy et al. [Phys. Rev. Lett. 102, 067206 (2009)], and the CPMF frequency plays the role of the current

Spin transfer torque enhancement in dual spin valve in the ballistic regime

The spin transfer torque in all-metal dual spin valve, in which two antiparallelly aligned pinned ferromagnetic layers are on the two sides of a free ferromagnetic layer with two thin nonmagnetic spacers in between, is studied in the ballistic regime. It is argued that, similar to the results in the diffusion regime, the spin transfer torque is dramatically enhanced in comparison to that in a conventional spin valve although no spin accumulation exists at the magnetic-nonmagnetic interfaces. Within the Slonczewski's approach, an analytical expression of the torque on the free magnetic layer is obtained, which may serve as a theoretical model for the micromagnetic simulation of the spin dynamics in dual spin valve. Depending on the orientation of free layer and the degree of electron polarization, the spin transfer torque enhancement could be tens times. The general cases when transmission and reflection probabilities of free layer are different from zero or one are also numerically calculated.Comment: 8 pages, 5 figure

Euler equation of the optimal trajectory for the fastest magnetization reversal of nano-magnetic structures

Based on the modified Landau-Lifshitz-Gilbert equation for an arbitrary Stoner particle under an external magnetic field and a spin-polarized electric current, differential equations for the optimal reversal trajectory, along which the magnetization reversal is the fastest one among all possible reversal routes, are obtained. We show that this is a Euler-Lagrange problem with constrains. The Euler equation of the optimal trajectory is useful in designing a magnetic field pulse and/or a polarized electric current pulse in magnetization reversal for two reasons. 1) It is straightforward to obtain the solution of the Euler equation, at least numerically, for a given magnetic nano-structure characterized by its magnetic anisotropy energy. 2) After obtaining the optimal reversal trajectory for a given magnetic nano-structure, finding a proper field/current pulse is an algebraic problem instead of the original nonlinear differential equation

Optimal time-dependent polarized current pattern for fast domain wall propagation in nanowires: Exact solutions for biaxial and uniaxial anisotropies

One of the important issues in nanomagnetism is to lower the current needed for a technologically useful domain wall (DW) propagation speed. Based on the modified Landau-Lifshitz-Gilbert (LLG) equation with both Slonczewski spin-transfer torque and the field-like torque, we derive the optimal spin current pattern for fast DW propagation along nanowires. Under such conditions, the DW velocity in biaxial wires can be enhanced as much as ten times compared to the velocities achieved in experiments so far. Moreover, the fast variation of spin polarization can help DW depinning. Possible experimental realizations are discussed.Comment: 4 pages, 1 figur

Geochemistry and petrogenesis of volcanic rocks from Daimao Seamount (South China Sea) and their tectonic implications

The South China Sea (SCS) experienced three episodes of seafloor spreading and left three fossil spreading centers presently located at 18°N, 17°N and 15.5°N. Spreading ceased at these three locations during magnetic anomaly 10, 8, and 5c, respectively. Daimao Seamount (16.6. Ma) was formed 10. my after the cessation of the 17°N spreading center. Volcaniclastic rocks and shallow-water carbonate facies near the summit of Daimao Seamount provide key information on the seamount's geologic history. New major and trace element and Sr-Nd-Pb isotopic compositions of basaltic breccia clasts in the volcaniclastics suggest that Daimao and other SCS seamounts have typical ocean island basalt-like composition and possess a 'Dupal' isotopic signature. Our new analyses, combined with available data, indicate that the basaltic foundation of Daimao Seamount was formed through subaqueous explosive volcanic eruptions at 16.6. Ma. The seamount subsided rapidly (>. 0.12. mm/y) at first, allowing the deposition of shallow-water, coral-bearing carbonates around its summit and, then, at a slower rate (<. 0.12. mm/y). We propose that the parental magmas of SCS seamount lavas originated from the Hainan mantle plume. In contrast, lavas from contemporaneous seamounts in other marginal basins in the western Pacific are subduction-related

Domain wall propagation through spin wave emission

We theoretically study field-induced domain wall (DW) motion in an electrically insulating ferromagnet with hard- and easy-axis anisotropies. DWs can propagate along a dissipationless wire through spin wave emission locked into the known soliton velocity at low fields. In the presence of damping, the mode appears before the Walker breakdown field for strong out-of-plane magnetic anisotropy, and the usual Walker rigid-body propagation mode becomes unstable when the field is between the maximal-DW-speed field and Walker breakdown field.Comment: 4 pages, 4 figure

Electron Delocalization in Gate-Tunable Gapless Silicene

The application of a perpendicular electric field can drive silicene into a gapless state, characterized by two nearly fully spin-polarized Dirac cones owing to both relatively large spin-orbital interactions and inversion symmetry breaking. Here we argue that since inter-valley scattering from non-magnetic impurities is highly suppressed by time reversal symmetry, the physics should be effectively single-Dirac-cone like. Through numerical calculations, we demonstrate that there is no significant backscattering from a single impurity that is non-magnetic and unit-cell uniform, indicating a stable delocalized state. This conjecture is then further confirmed from a scaling of conductance for disordered systems using the same type of impurities.Comment: 6 pages, 3 figures, published versio