SPring-8, the large synchrotron radiation facility

Figure 1：Schematic diagrams of spin-gapless semiconductor and anomalous X-ray diffraction. It was expected that the alloy thin film with spin-gapless semiconducting characteristics grown by molecular beam epitaxy in this study would have the XA structure. However, the image from a scanning transmission electron microscope showed that the film consists of two crystalline phases of similar compositions. According to anomalous X-ray diffraction, which can distinguish between different elements, the film exhibits disordered structures in which Co and Mn are interchanged with each other instead of the XA structure.

Figure 2：Results of anomalous X-ray diffraction analysis (top) and determined crystal structures (bottom).

*1. Heusler alloys
Heusler alloys are typical ordered alloys with the molecular formula X₂YZ. Half-Heusler alloys with the molecular formula XYZ have also been studied for a long time. Since 1903, when Friedrich Heusler reported that an alloy composed of three elements, non-magnetic Cu, Mn, and Al, exhibits ferromagnetic properties, various unique magnetic properties of Heusler alloys have been discovered. These include half-metallic properties, the magnetoresistance effect, magnetostriction, magnetic refrigeration, and shape memory effect. Heusler alloys have been studied and applied in a wide variety of areas including spintronics.

*2. Spin-gapless semiconductors
In the band theory of solids, materials with conduction electrons that are 100% spin-polarized are called half metals. Materials having semiconductive properties in addition to half-metallic properties are called spin-gapless semiconductors. Spin-gapless semiconductors are attracting attention as materials for spintronics devices because of their high polarizability and high mobility.

*3. Spintronics
Spintronics is an area of research targeting the technological application of both the electric charges and the spins representing the internal degrees of freedom of electrons in a solid material. Spintronics was coined from “spin” and “electronics”. Currently used spintronics devices include reading heads for hard discs featuring the giant magnetoresistance effect.

*4. Large synchrotron radiation facility SPring-8
SPring-8, owned by RIKEN, is a large synchrotron radiation facility that delivers some of the most powerful synchrotron radiations in the world. It is located in Harima Science Garden City, Hyogo Prefecture, Japan. JASRI supports users of the facility. The name “SPring-8” is derived from “Super Photon ring-8 GeV”. The research conducted at SPring-8 covers a wide range of fields including nanotechnology, biotechnology, and industrial applications.

*5. Anomalous X-ray diffraction
The scattering power of elements for X-rays of certain energies varies significantly owing to the resonance effect, which is known as the anomalous dispersion effect. Anomalous X-ray diffraction is a technique of measuring the X-ray energy dependence of the diffraction intensity of target elements using the wavelength selectivity (energy selectivity) of synchrotron radiation. Japanese scientists have contributed to this area since its early stages when the phenomenon of X-ray diffraction was discovered. In a well-known study, Dr. Shoji Nishikawa used anomalous X-ray diffraction to determine the polarity of non-centrosymmetric zinc sulfide crystals.