Heusler Alloys
Introduction
Heusler alloys are a class of ferromagnetic materials, named after the German scientist Fritz Heusler. They are ternary metallic alloys, typically composed of two transition metals and one main group element. These alloys are known for their unique properties such as high magnetoresistance, superconductivity, and thermoelectricity, making them highly useful in various technological applications.
History
The discovery of Heusler alloys dates back to 1903 when Fritz Heusler observed that an alloy of copper, aluminum, and manganese exhibited ferromagnetic properties despite none of the individual elements being ferromagnetic. This finding led to the development of a new class of materials, now known as Heusler alloys.
Structure and Composition
Heusler alloys are typically composed of two transition metals and one main group element, forming a cubic lattice structure. The most common type of Heusler alloy, known as a full-Heusler alloy, follows the formula X2YZ, where X and Y are transition metals and Z is a main group element. There are also half-Heusler alloys, which follow the XYZ formula and have a slightly different crystal structure.
Properties
Heusler alloys are known for their unique properties, which can be tuned by varying the composition of the alloy. These properties include high magnetoresistance, superconductivity, and thermoelectricity.
Magnetoresistance
Heusler alloys exhibit high magnetoresistance, a property that makes them useful in magnetic sensors and data storage devices. This property is due to the spin-dependent scattering of electrons in the alloy.
Superconductivity
Certain Heusler alloys, such as those containing mercury or lead, exhibit superconductivity at low temperatures. This property is due to the formation of Cooper pairs, which allow for the unimpeded flow of electric current.
Thermoelectricity
Heusler alloys can also exhibit thermoelectric properties, converting temperature differences into electric voltage. This property is useful in power generation and cooling applications.
Applications
Due to their unique properties, Heusler alloys find use in a variety of technological applications. These include magnetic sensors, data storage devices, superconductors, and thermoelectric devices.