Heusler compound

Heusler compounds are magnetic intermetallics with face-centered cubic crystal structure and a composition of XYZ (half-Heuslers) or X2YZ (full-Heuslers), where X and Y are transition metals and Z is in the p-block. The term derives from the name of German mining engineer and chemist Friedrich Heusler, who studied such a compound (Cu2MnAl) in 1903. Many of these compounds exhibit properties relevant to spintronics, such as magnetoresistance, variations of the Hall effect, ferro-, antiferro-, and ferrimagnetism, half- and semimetallicity, semiconductivity with spin filter ability, superconductivity, topological band structure and are actively studied as Thermoelectric materials. Their magnetism results from a double-exchange mechanism between neighboring magnetic ions. Manganese, which sits at the body centers of the cubic structure, was the magnetic ion in the first Heusler compound discovered. (See the Bethe–Slater curve for details of why this happens.) Depending on the field of literature being surveyed, one might encounter the same compound referred to with different chemical formulas. An example of the most common difference is X2YZ versus XY2Z, where the reference to the two transition metals X and Y in the compound are swapped. The traditional convention X2YZ arises from the interpretation of Heuslers as intermetallics and used predominantly in literature studying magnetic applications of Heuslers compounds. The XY2Z convention on the other hand is used mostly in thermoelectric materials and transparent conducting applications literature where semiconducting Heuslers (most half-Heuslers are semiconductors) are used. This convention, in which the left-most element on the periodic table comes first, uses the Zintl interpretation of semiconducting compounds where the chemical formula XY2Z is written in order of increasing electronegativity. In well-known compounds such as Fe2VAl which were historically thought of as metallic (semi-metallic) but were more recently shown to be small-gap semiconductors one might find both styles being used.