Spin engineering

Spin engineering describes the control and manipulation of quantum spin systems to develop devices and materials. This includes the use of the spin degrees of freedom as a probe for spin based phenomena. Because of the basic importance of quantum spin for physical and chemical processes, spin engineering is relevant for a wide range of scientific and technological applications. Current examples range from Bose–Einstein condensation to spin-based data storage and reading in state-of-the-art hard disk drives, as well as from powerful analytical tools like nuclear magnetic resonance spectroscopy and electron paramagnetic resonance spectroscopy to the development of magnetic molecules as qubits and magnetic nanoparticles. In addition, spin engineering exploits the functionality of spin to design materials with novel properties as well as to provide a better understanding and advanced applications of conventional material systems. Many chemical reactions are devised to create bulk materials or single molecules with well defined spin properties, such as a single-molecule magnet. The aim of this article is to provide an outline of fields of research and development where the focus is on the properties and applications of quantum spin.

As spin is one of the fundamental quantum properties of elementary particles it is relevant for a large range of physical and chemical phenomena. For instance, the spin of the electron plays a key role in the electron configuration of atoms which is the basis of the periodic table of elements. The origin of ferromagnetism is also closely related to the magnetic moment associated with the spin and the spin-dependent Pauli exclusion principle. Thus, the engineering of ferromagnetic materials like mu-metals or Alnico at the beginning of the last century can be considered as early examples of spin engineering, although the concept of spin was not yet known at that time. Spin engineering in its generic sense became possible only after the first experimental characterization of spin in the Stern–Gerlach experiment in 1922 followed by the development of relativistic quantum mechanics by Paul Dirac. This theory was the first to accommodate the spin of the electron and its magnetic moment.

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