Current-induced crystallisation in Heusler alloy films for memory potentiation in neuromorphic computation.

The current information technology has been developed based on von Neumann type computation. In order to sustain the rate of development, it is essential to investigate alternative technologies. In a next-generation computation, an important feature is memory potentiation, which has been overlooked to date.

Resolution of non-destructive imaging by controlled acceleration voltage in scanning electron microscopy.

A new method of non-destructive sub-surface interfacial characterisation has been developed recently, which can be useful for quality assurance of a buried interface in nanoelectronic devices, such as magnetic random access memory. Since the cell size of these devices have been reducing their sizes, it is important to evaluate the resolution of the non-destructive imaging. A sub nanometric layer of different materials such as W and Pt was grown underneath a capping layer with controlled thickness for the evaluation of their sizes in this study.

Global snapshot of the effects of the COVID-19 pandemic on the research activities of materials scientists between Spring and Autumn 2020.

We conducted a global survey on the effects of the COVID-19 pandemic on the research activities of materials scientists by distributing a questionnaire on 9 October 2020 with a response deadline of 23 October 2020. The questions covered issues such as access to labs, effectiveness of online conferences, and effects on doctoral students for the period covering the first lockdowns until the relaxation of restrictions in late September 2020 in many countries. The survey also included online interviews with eminent materials scientists who shared their local experiences during this period.

Discrimination of skyrmion chirality via spin-orbit and -transfer torques for logic operation.

Recently many works on magnetic memories and logic circuits, which use a magnetic skyrmion have been reported. Previously we micromagnetically simulated a method to switch a chirality of a magnetic skyrmion formed in a magnetic thin film by introducing a pulsed heat spot. In this paper, we propose a method to discriminate the chirality of a skyrmion in a branched nanowire by using spin-orbit torque (SOT) and spin-transfer torque (STT), and confirm the validity of the method by using simulation.

Switching of Skyrmion chirality by local heating.

Magnetic Skyrmions are energetically stable entities formed in a ferromagnet with a diameter of typically below 100 nm and are easily displaceable using an electrical current of 10 A/cm, resulting the Skyrmions to be more advantageous than domain walls for spintronic memory applications. Here, we demonstrated switching of a chirality of magnetic Skyrmions formed in magnetic thin films by introducing a pulsed heat spot using micromagnetic simulation. Skyrmions are found to expand with a pulsed heat spot, which induces the magnetic moments surrounding the Skyrmion to rotate by this expansion, followed by the chirality switching of the Skyrmion.

Chemical and structural analysis on magnetic tunnel junctions using a decelerated scanning electron beam.

Current information technology relies on the advancement of nanofabrication techniques. For instance, the latest computer memories and hard disk drive read heads are designed with a 12 nm node and 20 nm wide architectures, respectively. With matured nanofabrication processes, a yield of such nanoelectronic devices is typically up to about 90%.

Magneto-optical detection of spin accumulation under the influence of mechanical rotation.

The generation of spin-polarised carriers in a non-magnetic material holds the key to realise highly efficient spintronic devices. Recently, it has been shown that the large spin-orbit coupling can generate spin-polarised currents in noble metals such as tungsten and platinum. Especially, if small samples of such metals are rotated on a plane disc in the presence of a perpendicular magnetic field, the orbital angular momentum is altered leading to a segregation of spin up and spin down electrons, i.

Perpendicular Magnetic Anisotropy in Heusler Alloy Films and Their Magnetoresistive Junctions.

For the sustainable development of spintronic devices, a half-metallic ferromagnetic film needs to be developed as a spin source with exhibiting 100% spin polarisation at its Fermi level at room temperature. One of the most promising candidates for such a film is a Heusler-alloy film, which has already been proven to achieve the half-metallicity in the bulk region of the film. The Heusler alloys have predominantly cubic crystalline structures with small magnetocrystalline anisotropy.

Fabrication of Epitaxial FeO Film on a Si(111) Substrate.

The application of magnetic oxides in spintronics has recently attracted much attention. The epitaxial growth of magnetic oxide on Si could be the first step of new functional spintronics devices with semiconductors. However, epitaxial spinel ferrite films are generally grown on oxide substrates, not on semiconductors.

Highly Efficient Spin-Current Operation in a Cu Nano-Ring.

An all-metal lateral spin-valve structure has been fabricated with a medial Copper nano-ring to split the diffusive spin-current path. We have demonstrated significant modulation of the non-local signal by the application of a magnetic field gradient across the nano-ring, which is up to 30% more efficient than the conventional Hanle configuration at room temperature. This was achieved by passing a dc current through a current-carrying bar to provide a locally induced Ampère field.

Realisation of magnetically and atomically abrupt half-metal/semiconductor interface: CoFeSiAl/Ge(111).

Halfmetal-semiconductor interfaces are crucial for hybrid spintronic devices. Atomically sharp interfaces with high spin polarisation are required for efficient spin injection. In this work we show that thin film of half-metallic full Heusler alloy CoFeSiAl with uniform thickness and B2 ordering can form structurally abrupt interface with Ge(111).

Non-destructive imaging of buried electronic interfaces using a decelerated scanning electron beam.

Recent progress in nanotechnology enables the production of atomically abrupt interfaces in multilayered junctions, allowing for an increase in the number of transistors in a processor. However, uniform electron transport has not yet been achieved across the entire interfacial area in junctions due to the existence of local defects, causing local heating and reduction in transport efficiency. To date, junction uniformity has been predominantly assessed by cross-sectional transmission electron microscopy, which requires slicing and milling processes that can potentially introduce additional damage and deformation.

Controlling the half-metallicity of Heusler/Si(1 1 1) interfaces by a monolayer of Si-Co-Si.

By using first-principles calculations we show that the spin-polarization reverses its sign at atomically abrupt interfaces between the half-metallic Co2(Fe,Mn)(Al,Si) and Si(1 1 1). This unfavourable spin-electronic configuration at the Fermi-level can be completely removed by introducing a Si-Co-Si monolayer at the interface. In addition, this interfacial monolayer shifts the Fermi-level from the valence band edge close to the conduction band edge of Si.

The Effect of Cobalt-Sublattice Disorder on Spin Polarisation in Co₂FeMnSi Heusler Alloys.

In this work we present a theoretical study of the effect of disorder on spin polarisation at the Fermi level, and the disorder formation energies for Co₂FeMnSi (CFMS) alloys. The electronic calculations are based on density functional theory with a Hubbard U term. Chemical disorders studied consist of swapping Co with Fe/Mn and Co with Si; in all cases we found these are detrimental for spin polarisation, .

Growth and characterization of thin Cu-phthalocyanine films on MgO(001) layer for organic light-emitting diodes.

Surface morphology and thermal stability of Cu-phthalocyanine (CuPc) films grown on an epitaxially grown MgO(001) layer were investigated by using atomic force microscope and X-ray diffractometer. The (002) textured β phase of CuPc films were prepared at room temperature beyond the epitaxial MgO/Fe/MgO(001) buffer layer by the vacuum deposition technique. The CuPc structure remained stable even after post-annealing at 350°C for 1 h under vacuum, which is an important advantage of device fabrication.