Spin polarization
Encyclopedia
Spin polarization is the degree to which the spin
, i.e., the intrinsic angular momentum
of elementary particles, is aligned with a given direction. This property may pertain to the spin, hence to the magnetic moment
, of conduction electrons in ferromagnetic metals, such as iron
, giving rise to spin-polarized currents. It may refer to (static) spin waves, preferential correlation
of spin orientation with ordered lattices (semiconductors or insulators).
It may also pertain to beams of particles, produced for particular aims, such as polarized neutron scattering or muon spin spectroscopy
. Spin polarization of electrons or of nuclei, often called simply magnetization
, is also produced by the application of a magnetic field
. Curie law is used to produce an induction signal in Electron spin resonance (ESR or EPR) and in Nuclear magnetic resonance
(NMR).
Spin polarization is also important for spintronics
, a branch of electronics
. Magnetic semiconductor
s are being researched as possible spintronic materials.
The spin of free electrons is measured either by a LEED image from a clean wolfram
-crystal (SPLEED) or by an electron microscope
composed purely of electrostatic lenses and a gold
foil as a sample. Back scattered electrons are decelerated by annular optics and focused onto a ring shaped electron mulitplier at about 15°. The position on the ring is recorded. This whole device is called a Mott-detector
. Depending on their spin the electrons have the chance to hit the ring at different positions. 1% of the electrons are scattered in the foil. Of these 1% are collected by the detector and then about 30% of the electrons hit the detector at the wrong position. Both devices work due to spin orbit coupling.
The circular polarization
of electromagnetic fields is due to spin polarization of their constituent photons.
In the most generic context, spin polarization is any alignment of the components of a non-scalar
(vectorial, tensorial, spinor) field with its arguments, i.e., with the nonrelativistic three spatial or
relativistic four spatiotemporal regions over which it is defined. In this sense, it also includes
gravitational waves and any field theory that couples its constituents with the differential
operators of vector analysis.
Spin (physics)
In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...
, i.e., the intrinsic angular momentum
Angular momentum
In physics, angular momentum, moment of momentum, or rotational momentum is a conserved vector quantity that can be used to describe the overall state of a physical system...
of elementary particles, is aligned with a given direction. This property may pertain to the spin, hence to the magnetic moment
Magnetic moment
The magnetic moment of a magnet is a quantity that determines the force that the magnet can exert on electric currents and the torque that a magnetic field will exert on it...
, of conduction electrons in ferromagnetic metals, such as iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
, giving rise to spin-polarized currents. It may refer to (static) spin waves, preferential correlation
of spin orientation with ordered lattices (semiconductors or insulators).
It may also pertain to beams of particles, produced for particular aims, such as polarized neutron scattering or muon spin spectroscopy
Muon spin spectroscopy
Muon spin spectroscopy is an experimental technique based on the implantation of spin-polarized muons in matter and on the detection of the influence of the atomic, molecular or crystalline surroundings on their spin motion...
. Spin polarization of electrons or of nuclei, often called simply magnetization
Magnetization
In classical electromagnetism, magnetization or magnetic polarization is the vector field that expresses the density of permanent or induced magnetic dipole moments in a magnetic material...
, is also produced by the application of a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
. Curie law is used to produce an induction signal in Electron spin resonance (ESR or EPR) and in 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...
(NMR).
Spin polarization is also important for spintronics
Spintronics
Spintronics , also known as magnetoelectronics, is an emerging technology that exploits both the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-state devices.An additional effect occurs when a spin-polarized current is...
, a branch of electronics
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
. Magnetic semiconductor
Magnetic semiconductor
Magnetic semiconductors are semiconductor materials that exhibit both ferromagnetism and useful semiconductor properties. If implemented in devices, these materials could provide a new type of control of conduction...
s are being researched as possible spintronic materials.
The spin of free electrons is measured either by a LEED image from a clean wolfram
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
-crystal (SPLEED) or by an electron microscope
Electron microscope
An electron microscope is a type of microscope that uses a beam of electrons to illuminate the specimen and produce a magnified image. Electron microscopes have a greater resolving power than a light-powered optical microscope, because electrons have wavelengths about 100,000 times shorter than...
composed purely of electrostatic lenses and a gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
foil as a sample. Back scattered electrons are decelerated by annular optics and focused onto a ring shaped electron mulitplier at about 15°. The position on the ring is recorded. This whole device is called a Mott-detector
Nevill Francis Mott
Sir Nevill Francis Mott, CH, FRS was an English physicist. He won the Nobel Prize for Physics in 1977 for his work on the electronic structure of magnetic and disordered systems, especially amorphous semiconductors. The award was shared with Philip W. Anderson and J. H...
. Depending on their spin the electrons have the chance to hit the ring at different positions. 1% of the electrons are scattered in the foil. Of these 1% are collected by the detector and then about 30% of the electrons hit the detector at the wrong position. Both devices work due to spin orbit coupling.
The circular polarization
Circular polarization
In electrodynamics, circular polarization of an electromagnetic wave is a polarization in which the electric field of the passing wave does not change strength but only changes direction in a rotary type manner....
of electromagnetic fields is due to spin polarization of their constituent photons.
In the most generic context, spin polarization is any alignment of the components of a non-scalar
(vectorial, tensorial, spinor) field with its arguments, i.e., with the nonrelativistic three spatial or
relativistic four spatiotemporal regions over which it is defined. In this sense, it also includes
gravitational waves and any field theory that couples its constituents with the differential
operators of vector analysis.