Heusler alloy
As Heusler alloys, named after Friedrich Heusler alloys are referred to in the metallurgy, containing, as an essential part of a Heusler phase. Heusler phases are intermetallics with special composition and lattice structure. They are ferromagnetic, although the alloying elements contained therein do not have this property. Heusler described this phenomenon in 1903 first to Cu2MnAl.
Heusler compounds show other properties, as one would expect from the combination of the alloy components: The first Heusler compound consisted of the non-magnetic elements copper, manganese and aluminum. However, Cu2MnAl is a ferromagnetic, even at room temperature.
Structure and properties
There are two types of Heusler alloys. The half- Heusler alloys generally have a composition XYZ ( each letter stands for an alloying element ), while the full Heusler alloys are composed according to the formula X2YZ. While X and Y are the transition metals, while Z is an element of III.-V. Main group. The alloying elements form ordered phases, so that the crystal structure of four (at the XYZ type is one unoccupied ) nested face-centered cubic sublattices is. The still not understood in detail interactions between the atoms of sublattice cause an almost complete alignment (spin polarization ) of the magnetic dipole moments of the "right polarized " component ( eg spin ) of the electron, while the " wrong polarized " electrons ( z. B.) are all non-metallic. which macroscopically at sufficiently low temperatures (eg room temperature or below ) expressed as ferromagnetism. So you have to do it with so-called half- metallic ferromagnetism.
Use as a topological insulator
In 2006 Shoucheng Zhang said at the Stanford University requires a new quantum state of matter for the semiconductor mercury cadmium telluride (HgTe ). Physicist Laurens W. Molenkamp order confirmed at the University of Würzburg the assumption experimentally. Topological insulators are made of materials that, while insulators or semiconductors, act on the surface or at the interfaces, but metallic. They differ in this case from normal metals, since the electrons do not interact with the area as superconductors at the surface or at interfaces, as they are in a new quantum state. Unlike superconductors, topological insulators have two non-interacting currents, one for each spin direction. Both spin currents, which are not affected by defects or impurities in the material can be used for information processing. Of the Heusler compounds more than 1,000 known suspected topological insulators for more than 50 features.