Spin polarization

In <a href="/facts/Particle_physics/YgIuyj2t">particle physics</a>, spin polarization is the degree to which the <a href="/facts/Spin_(physics)/4Jvp7e8P">spin</a>, i.e., the intrinsic <a href="/facts/Angular_momentum/7TuSVFxq">angular momentum</a> of <a href="/facts/Elementary_particle/CTFDM97U">elementary particles</a>, is aligned with a given direction. This property may pertain to the spin, hence to the <a href="/facts/Magnetic_moment/VpAQKJtr">magnetic moment</a>, of <a href="/facts/Conduction_electrons/2NUALlHJ">conduction electrons</a> in <a href="/facts/Ferromagnet/fH3HFnSl">ferromagnetic</a> metals, such as <a href="/facts/Iron/QK1JYy8E">iron</a>, giving rise to spin-polarized <a href="/facts/Current_(electricity)/Dc1xdnUX">currents</a>. It may refer to (static) <a href="/facts/Spin_waves/bgSrTqEc">spin waves</a>, preferential correlation of spin orientation with ordered lattices (<a href="/facts/Semiconductor/zFf3mGTE">semiconductors</a> or <a href="/facts/Insulator_(electricity)/SfSXkrh5">insulators</a>).
It may also pertain to beams of particles, produced for particular aims, such as polarized neutron scattering or <a href="/facts/Muon_spin_spectroscopy/yQa2YyVF">muon spin spectroscopy</a>. Spin polarization of <a href="/facts/Electron/L0KBo5cW">electrons</a> or of <a href="/facts/Atomic_nucleus/orpIm5Xl">nuclei</a>, often called simply <a href="/facts/Magnetization/zxrtXzTN">magnetization</a>, is also produced by the application of a <a href="/facts/Magnetic_field/Ta8Ev588">magnetic field</a>. <a href="/facts/Curie_law/em3ucVMB">Curie law</a> is used to produce an induction signal in <a href="/facts/Electron_spin_resonance/TDHV8c9e">electron spin resonance</a> (ESR or EPR) and in <a href="/facts/Nuclear_magnetic_resonance/pGYAn9Bz">nuclear magnetic resonance</a> (NMR).
Spin polarization is also important for <a href="/facts/Spintronics/dAWl8rcI">spintronics</a>, a branch of <a href="/facts/Electronics/E4JhgISq">electronics</a>. <a href="/facts/Magnetic_semiconductor/fTxchWPj">Magnetic semiconductors</a> are being researched as possible spintronic materials.
The spin of free electrons is measured either by a <a href="/facts/Low-energy_electron_diffraction/vaAuSE7k">LEED</a> image from a clean <a href="/facts/Tungsten/WYwbNDYX">wolfram</a>-crystal (SPLEED) or by an <a href="/facts/Electron_microscope/XtaBktwF">electron microscope</a> composed purely of electrostatic lenses and a <a href="/facts/Gold/1znknojp">gold</a> foil as a sample. Back scattered electrons are decelerated by annular optics and focused onto a ring shaped electron multiplier at about 15°. The position on the ring is recorded. This whole device is called a <a href="/facts/Nevill_Francis_Mott/r1xrUSDh">Mott-detector</a>. 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 <a href="/facts/Circular_polarization/fYQvT0mI">circular polarization</a> of electromagnetic fields is due to spin polarization of their constituent <a href="/facts/Photons/mFNhAEzA">photons</a>.
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 <a href="/facts/Gravitational_waves/4XWN3NtG">gravitational waves</a> and any field theory that couples its constituents with the differential operators of vector analysis.

Spin polarization open-in-new

Spin polarization