Spin Engineering
Encyclopedia
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 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.
s 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-metal
s 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.
Whereas the physics of spin engineering dates back to the groundbreaking findings of quantum chemistry and physics within the first decades of the 20th century, the chemical aspects of spin engineering have received attention especially within the last twenty years. Today, researchers focus on specialized topics, such as the design and synthesis of molecular magnets or other model systems in order to understand and harness the fundamental principles behind phenomena such as the relation between magnetism and chemical reactivity as well as microstructure related mechanical properties of metals and the biochemical impact of spin (e. g. photoreceptor protein
s) and spin transport.
Degrees of freedom (physics and chemistry)
A degree of freedom is an independent physical parameter, often called a dimension, in the formal description of the state of a physical system...
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
Nuclear magnetic resonance
Nuclear magnetic resonance is a physical phenomenon in which magnetic nuclei in a magnetic field absorb and re-emit electromagnetic radiation...
spectroscopy and electron paramagnetic resonance
Electron paramagnetic resonance
Electron paramagnetic resonance or electron spin resonance spectroscopyis a technique for studying chemical species that have one or more unpaired electrons, such as organic and inorganic free radicals or inorganic complexes possessing a transition metal ion...
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 single-molecule magnet
Single-molecule magnet
Single-molecule magnets or SMMs are a class of metalorganic compounds, that show superparamagnetic behavior below a certain blocking temperature at the molecular scale. In this temperature range, SMMs exhibit magnetic hysteresis of purely molecular origin...
.
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.
Introduction
As spin is one of the fundamental quantum properties of elementary particleElementary particle
In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not known to be made up of smaller particles. If an elementary particle truly has no substructure, then it is one of the basic building blocks of the universe from which...
s it is relevant for a large range of physical and chemical phenomena. For instance, the spin of the electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
plays a key role in the electron configuration
Electron configuration
In atomic physics and quantum chemistry, electron configuration is the arrangement of electrons of an atom, a molecule, or other physical structure...
of atoms which is the basis of the periodic table of elements. The origin of ferromagnetism
Ferromagnetism
Ferromagnetism is the basic mechanism by which certain materials form permanent magnets, or are attracted to magnets. In physics, several different types of magnetism are distinguished...
is also closely related to the magnetic moment associated with the spin and the spin-dependent Pauli exclusion principle
Pauli exclusion principle
The Pauli exclusion principle is the quantum mechanical principle that no two identical fermions may occupy the same quantum state simultaneously. A more rigorous statement is that the total wave function for two identical fermions is anti-symmetric with respect to exchange of the particles...
. Thus, the engineering of ferromagnetic materials like mu-metal
Mu-metal
Mu-metal is a nickel-iron alloy that is notable for its high magnetic permeability. The high permeability makes mu-metal very effective at screening static or low-frequency magnetic fields, which cannot be attenuated by other methods. The name came from the Greek letter mu which represents...
s or Alnico
Alnico
Alnico is an acronym referring to iron alloys which in addition to iron are composed primarily of aluminium , nickel and cobalt , hence al-ni-co, with the addition of copper, and sometimes titanium. Alnico alloys are ferromagnetic, with a high coercivity and are used to make permanent magnets...
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.
Whereas the physics of spin engineering dates back to the groundbreaking findings of quantum chemistry and physics within the first decades of the 20th century, the chemical aspects of spin engineering have received attention especially within the last twenty years. Today, researchers focus on specialized topics, such as the design and synthesis of molecular magnets or other model systems in order to understand and harness the fundamental principles behind phenomena such as the relation between magnetism and chemical reactivity as well as microstructure related mechanical properties of metals and the biochemical impact of spin (e. g. photoreceptor protein
Photoreceptor protein
Photoreceptors are light-sensitive proteins involved in the sensing and response to light in a variety of organisms. Some examples are rhodopsin in the photoreceptor cells of the vertebrate retina, phytochrome in plants, and bacteriorhodopsin and bacteriophytochromes in some bacteria...
s) and spin transport.
Spintronics
Spintronics is the exploitation of both the intrinsic spin of the electron and its fundamental electronic charge in solid-state devices and is thus a part of spin engineering. Spintronics is probably one of the most advanced fields of spin engineering with many important inventions which can be found in end-user devices like the reading heads for magnetic hard disk drives. This section is divided in basic spintronic phenomena and their applications.Basic spintronic phenomena
- Giant magnetoresistance (GMR), Tunnel magnetoresistance (TMR)Tunnel magnetoresistanceThe Tunnel magnetoresistance is a magnetoresistive effect that occurs in magnetic tunnel junctions . This is a component consisting of two ferromagnets separated by a thin insulator. If the insulating layer is thin enough , electrons can tunnel from one ferromagnet into the other...
, Spin valveSpin valveA spin valve is a device consisting of two or more conducting magnetic materials, that alternates its electrical resistance depending on the alignment of the magnetic layers, in order to exploit the Giant Magnetoresistive effect. The magnetic layers of the device align "up" or "down" depending on... - Spin transfer torque (STT)Spin torque transferSpin-transfer torque is an effect in which the orientation of a magnetic layer in a tunnel magnetoresistance or spin valve can be modified using a spin-polarized current....
- Spin injection
- Pure spin currents
- Spin pumpingSpin pumpingSpin pumping is a method of generating a spin current, the spintronic analog of a battery in conventional electronics.In order to make a spintronic device, the primary requirement is to have a system that can generate a current of spin-polarized electrons, as well as a system that is sensitive to...
- Spin waveSpin waveSpin waves are propagating disturbances in the ordering of magnetic materials. These low-lying collective excitations occur in magnetic lattices with continuous symmetry. From the equivalent quasiparticle point of view, spin waves are known as magnons, which are boson modes of the spin lattice...
s, magnonicsMagnonicsMagnonics is an emerging field of modern magnetism, which can be considered a sub-field of modern solid state physics. Magnonics combines waves and magnetism, its main aim is to investigate the behaviour of spin waves in nano-structure elements. In essence, spin waves are a propagating re-ordering... - (inverse) Spin Hall effect
- Spin calorics, Spin Seebeck effect
Applications of spintronics
this section is devoted to current and possible future applications of spintronics which make use of one or the combination of several basic spintronic phenomena:- Hard disk drive read headsDisk read-and-write headDisk read/write heads are the small parts of a disk drive, that move above the disk platter and transform platter's magnetic field into electrical current or vice versa – transform electrical current into magnetic field...
- Magnetoresistive random access memory (MRAMMRAMMagnetoresistive Random-Access Memory is a non-volatile computer memory technology that has been under development since the 1990s. Continued increases in density of existing memory technologies – notably flash RAM and DRAM – kept it in a niche role in the market, but its proponents...
) - Racetrack memoryRacetrack memoryRacetrack memory is an experimental non-volatile memory device under development at IBM's Almaden Research Center by a team led by Stuart Parkin. In early 2008, a 3-bit version was successfully demonstrated...
- Spin transistorSpin transistorThe magnetically-sensitive transistor , originally proposed in 1990 and currently still being developed, is an improved design on the common transistor invented in the 1940s...
- Spin quantum computingQuantum computerA quantum computer is a device for computation that makes direct use of quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data. Quantum computers are different from traditional computers based on transistors...
- MagnonMagnonA magnon is a collective excitation of the electrons' spin structure in a crystal lattice. In contrast, a phonon is a collective excitation of the crystal lattice atoms or ions. In the equivalent wave picture of quantum mechanics, a magnon can be viewed as a quantized spin wave. As a...
-based spintronics
Spin Materials
materials which properties are determined or strongly influenced by quantum spin:- Magnetic alloys, i.e. Heusler alloyHeusler alloyA Heusler alloy is a ferromagnetic metal alloy based on a Heusler phase. Heusler phases are intermetallics with particular composition and face-centered cubic crystal structure. They are ferromagnetic—even though the constituting elements are not—as a result of the double-exchange mechanism between...
s - GrapheneGrapheneGraphene is an allotrope of carbon, whose structure is one-atom-thick planar sheets of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The term graphene was coined as a combination of graphite and the suffix -ene by Hanns-Peter Boehm, who described single-layer...
systems - Organic spin materials
- Molecular nanomagnets
- Magnetic molecules
- Organic radicals
- Metamaterilas with artificial magnetism
Spin based detection
methods to characterize materials and physical or chemical processes via spin based phenomena:- Magneto-optic Kerr effectMagneto-optic Kerr effectMagneto-optic Kerr effect is one of the magneto-optic effects. It describes the changes of light reflected from magnetized media.-Definition:The light that is reflected from a magnetized surface can change in both polarization and reflected intensity...
(MOKEMokeMoke may refer to:* Moke - archaic British, Australian, and United States slang meaning Donkey* Mini Moke - a utility vehicle produced by the British Motor Corporation * Moke - a British rock band...
) - Nuclear magnetic resonanceNuclear magnetic resonanceNuclear magnetic resonance is a physical phenomenon in which magnetic nuclei in a magnetic field absorb and re-emit electromagnetic radiation...
(NMRNMRNMR may refer to:Applications of Nuclear Magnetic Resonance:* Nuclear magnetic resonance* NMR spectroscopy* Solid-state nuclear magnetic resonance* Protein nuclear magnetic resonance spectroscopy* Proton NMR* Carbon-13 NMR...
) - Neutron scatteringNeutron scatteringNeutron scattering,the scattering of free neutrons by matter,is a physical processand an experimental technique using this processfor the investigation of materials.Neutron scattering as a physical process is of primordial importance...
- Spin polarized photoemission
- Brillouin Light Scattering (BLS)Brillouin scatteringBrillouin scattering, named after Léon Brillouin, occurs when light in a medium interacts with time dependent optical density variations and changes its energy and path. The density variations may be due to acoustic modes, such as phonons, magnetic modes, such as magnons, or temperature gradients...
- X-ray magnetic circular dichroism (XMCDXMCDX-ray magnetic circular dichroism is a difference spectrum of two x-ray absorption spectra taken in a magnetic field, one taken with left circularly polarized light, and one with right circularly polarized light...
)
External links
- Albert Fert (Nobel Prize in Physics (2007)), "The origin, the development and the future of spintronics", Nobel Lecture as pdf at nobelprize.org
- Peter Grünberg (Nobel Prize in Physics (2007)), "From spinwaves to Giant Magnetoresistance (GMR) and beyond", Nobel Lecture as pdf at nobelprize.org
- Scientific background of the discovery of the Giant Magnetoresistance, compiled by the Class for Physics of the Royal Swedish Academy of Sciences
- Animations of GMR Sensors at the IBM Research Homepage
- Albert Fert (Nobel Prize in Physics (2007)) video answer of the question: "What is spin?"
- Creation of a pure spin current in Graphene, article from Physorg.com