Electrical control of the ferromagnetic phase transition in cobalt at room temperature

Electrical control of magnetic properties is crucial for device applications in the field of spintronics. Although the magnetic coercivity or anisotropy has been successfully controlled electrically in metals as well as in semiconductors, the electrical control of Curie temperature has been realized only in semiconductors at low temperature. Here, we demonstrate the room-temperature electrical control of the ferromagnetic phase transition in cobalt, one of the most representative transition-metal ferromagnets. Solid-state field effect devices consisting of a ultrathin cobalt film covered by a dielectric layer and a gate electrode were fabricated. We prove that the Curie temperature of cobalt can be changed by up to 12 K by applying a gate electric field of about ±2 MV cm(-1). The two-dimensionality of the cobalt film may be relevant to our observations. The demonstrated electric field effect in the ferromagnetic metal at room temperature is a significant step towards realizing future low-power magnetic applications.     

Formation of Ultrafine‐Grained Microstructure of Ti–6Al–4V Alloy by Hot Deformation of α′ Martensite Starting Microstructure

We have presented a formation of ultrafine‐grained microstructure (d_α ≈ 0.2 µm) of industrial Ti–6Al–4V alloy produced by the hot compression of a sample with the acicular α′ martensite starting microstructure. The hot‐deformation behavior was different from the case of the conventional (α + β) starting microstructure, that is, the phase transformation of α′/(α + β) during hot working enhanced the microstructural conversion, especially under the conditions of a low temperature and a high‐strain rate.     

Plasma Start-up in HIT-II and NSTX Using Transient Coaxial Helicity Injection

The method of transient coaxial helicity injection (CHI) has previously been used in the HIT-II experiment at the University of Washington to produce 100 kA of closed flux current. The generation of the plasma current by CHI involves the process of magnetic reconnection, which has been experimentally controlled in the National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Laboratory to allow this potentially unstable phenomenon to reorganize the magnetic field lines to form closed, nested magnetic surfaces carrying a plasma current up to 160 kA. This is a world record for non-inductive closed-flux current generation, and demonstrates the high current capability of this method.     

Structural features of anodic oxide films formed on aluminum substrate coated with self-assembled microspheres

The structural features of anodic oxide films formed on an aluminum substrate coated with self-assembled microspheres were investigated by scanning electron microscopy and atomic force microscopy. In the first anodization in neutral solution, the growth of a barrier-type film was partially suppressed in the contact area between the spheres and the underlying aluminum substrate, resulting in the formation of ordered dimple arrays in an anodic oxide film. After the subsequent second anodization in acid solution at a voltage lower than that of the first anodization, nanopores were generated only within each dimple. The nanoporous region could be removed selectively by post-chemical etching using the difference in structural dimensions between the porous region and the surrounding barrier region. The mechanism of anodic oxide growth on the aluminum substrate coated with microspheres through multistep anodization is discussed.     

Atomic-scale cellular model and profile simulation of Si etching: Formation of surface roughness and residue

Formation mechanisms for profile anomalies such as surface roughness and residue have been investigated numerically and experimentally for Si etching in Cl₂/O₂ plasmas. The numerical simulation employed an atomic-scale cellular model (ASCeM) based on the Monte Carlo algorithm, which reproduced the feature profile evolution experimentally observed during etching at increased O₂ concentrations. A comparison between simulation and experiment indicated that the local surface oxidation induces surface roughness at the bottom of the feature during etching; then, synergistic effects between surface oxidation and ion scattering in microstructural features on roughened surfaces increase the surface roughness, which in turn causes a number of significant residues or micropillars on bottom surfaces of the feature. In practice, in roughened microstructural features, geometrical shadowing effects for neutral oxygen suppress the surface oxidation at the local feature bottom, where the energetic ion incidence is increased owing to ion scattering on sidewalls of the local feature.     

Spatial distribution and polarization dependence of the optical near-field in a silicon microfabricated probe

This paper reports on the spatial distribution and polarization behaviour of the optical near-field at the aperture of a Si micromachined probe. A sub-100 nm aperture at the apex of a SiO₂ tip on a Si cantilever was successfully fabricated by selective etching of the SiO₂ tip in a buffered-HF solution using a thin Cr film as a mask. The aperture, 10–100 nm in size, can be reproducibly fabricated by optimizing the etching time. The optical throughput of several apertures was measured. For a 100 nm aperture, a throughput of 1% was approved. The probe shows a very high optical throughput owing to the geometrical structure of the tip. The spatial distribution of the near-field light is measured and simulated using a finite difference-time domain method. The polarization behaviour of apertures with different shapes was analysed using a photon counting camera system.     

Fast magnetic reconnection with anomalous ion heating and its application

Magnetic reconnection of two toroidal plasmas with the third field component B_X parallel to the X-lines revealed a clear dependence of sheet-current resistivity and ion heating energy on the sheet-width normalized by the ion gyroradius. Initially, the effective resistivity of sheet-current stayed constant, but it increased significantly when the sheet was compressed shorter than the ion-gyroradius. The anomalous current-sheet dissipation was followed by large increase in ion outflow velocity and ion temperature. This anomalous effect caused both the reconnection speed and the ion heating energy to increase with external compression force and inversely with the B_X component. These properties of reconnection lead us to a new controlled plasma heating for various fusion plasmas and other industrial plasmas.