There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

5.1. Nanoalloys of Group 11 (Cu, Ag, Au) 865 5.1.1. Cu−Ag 866 5.1.2. Cu−Au 867 5.1.3. Ag−Au 870 5.1.4. Cu−Ag−Au 872 5.2. Nanoalloys of Group 10 (Ni, Pd, Pt) 872 5.2.1. Ni−Pd 872 * To whom correspondence should be addressed. Phone: +39010 3536214. Fax:+39010 311066. E-mail: ferrando@fisica.unige.it. † Universita di Genova. ‡ Argonne National Laboratory. § University of Birmingham. | As of October 1, 2007, Chemical Sciences and Engineering Division. Volume 108, Number 3

Nanoalloys: From Theory to Applications of Alloy Clusters and Nanoparticles

Spintronics is a multidisciplinary field involving physics, chemistry, and engineering, and is a new research area for solid-state scientists. A variety of new materials must be found to satisfy different demands. The search for ferromagnetic semiconductors and stable half-metallic ferromagnets with Curie temperatures higher than room temperature remains a priority for solid-state chemistry. A general understanding of structure-property relationships is a necessary prerequisite for the design of new materials. In this Review, the most important developments in the field of spintronics are described from the point of view of materials science.

Spintronics: a challenge for materials science and solid-state chemistry.

In this paper, we review the recent progress in the resistive random access memory (ReRAM) technology, one of the most promising emerging nonvolatile memories, in which both electronic and electrochemical effects play important roles in the nonvolatile functionalities. First, we provide a brief historical overview of the research in this field. We also provide a technological overview and the epoch-making achievements, followed by an account of the current understanding of both bipolar and unipolar ReRAM operations. Finally, we summarize the challenges facing the ReRAM technology as it moves toward the beyond-2X-nm generation of nonvolatile memories and the so-called beyond complementary metal-oxide-semiconductor (CMOS) device.

Resistive Random Access Memory (ReRAM) Based on Metal Oxides

The key methods for the preparation of magnetic nanoparticles are described systematically. The experimental data on their properties are analysed and generalised. The main theoretical views on the magnetism of nanoparticles are considered.

https://iopscience.iop.org/article/10.1070/RC2005v074n06ABEH000897/pdf

Magnetic nanoparticles: preparation, structure and properties

A new class of half-metallic ferromagnets has been found in the zinc-blende crystal structure. The previously nonexistent zinc-blende CrAs thin films have been synthesized on GaAs (001) substrates by molecular-beam epitaxy, and show a ferromagnetic behavior at room temperature. The zinc-blende CrAs has been designed by ab initio calculations based on the local spin-density approximation, and the calculation predicts the highly spin-polarized electronic band structure.

https://iopscience.iop.org/article/10.1143/JJAP.39.L1118/pdf

Material Design of Half-Metallic Zinc-Blende CrAs and the Synthesis by Molecular-Beam Epitaxy

We have succeeded in growing ferromagnetic metals (Co, Fe, and NiFe)/Al2O3/AlGaAs heterostructures with homogeneous flat interfaces. The electroluminescence from a light-emitting diode with a metal/insulator/semiconductor (MIS) structure depends on the magnetization direction of the ferromagnetic electrode. This fact shows that a spin injection from the ferromagnetic metal to the semiconductor is achieved. The spin-injection efficiency is estimated to be the order of 1% at room temperature.

Spin-polarized light-emitting diode using metal/insulator/semiconductor structures

Zinc-blende CrAs/GaAs multilayers were grown by molecular beam epitaxy. It was certified that each CrAs layer maintains an epitaxial relationship with the zinc-blende GaAs structure judging from the reflection high-energy electron diffraction observation. The film contains thicker zinc- blende CrAs layers in total than the CrAs thin film directly grown on the GaAs substrate which has the critical thickness of 3 nm. It was clarified that the optimum thicknesses of CrAs and GaAs to keep a good epitaxial relationship are 2 ML and 2 ML, respectively. The electronic structure of the multilayer is thought to be close to that of the (Ga, Cr)As thin film which has 50% of Cr content judging from x-ray absorption spectroscopy measurements.

Epitaxial growth of zinc-blende CrAs/GaAs multilayer

We have succeeded in demonstrating zero-magnetic-field spin injection in metal–insulator–semiconductor (MIS) structure at room temperature using FePt/MgO/GaAs-based light-emitting diode heterojunction with out-of-plane magnetization. The spin polarization was investigated by spin-polarized electroluminescence (EL). The lower estimate injected at remanence was 1.5% and that injected at 1 T was reached up to 11.5%. The spin injection efficiency was estimated at least 29%. The bias dependence of the EL circular polarization showed that it decreases with increasing bias voltage for both at 1 T and at remanence.

Electrical Spin Injection from Out-of-Plane Magnetized FePt/MgO Tunneling Junction into GaAs at Room Temperature

Gold (Au)∕semi-insulating (SI)-GaAs Schottky diode was fabricated by the standard photolithography method using wet etching. Magnetic-field-dependent avalanche breakdown phenomena were observed in the current–voltage curves measured under magnetic field. The avalanche breakdown due to impact ionization was postponed to higher electrical field under applied magnetic field. Accordingly, threshold voltages of avalanche breakdown increased with the applied magnetic field. Above 0.2T, avalanche breakdown was totally quenched. When Au‐SI‐GaAs Schottky diode was operated above the threshold voltage, giant mangetoresistive effects up to 100 000% were achieved under magnetic field of 0.8T.

Takashi Manago

Papers

Material Design of Half-Metallic Zinc-Blende CrAs and the Synthesis by Molecular-Beam Epitaxy

Spin-polarized light-emitting diode using metal/insulator/semiconductor structures

Epitaxial growth of zinc-blende CrAs/GaAs multilayer

Electrical Spin Injection from Out-of-Plane Magnetized FePt/MgO Tunneling Junction into GaAs at Room Temperature

Magnetic-field-controllable avalanche breakdown and giant magnetoresistive effects in Gold∕semi-insulating-GaAs Schottky diode