Spin polarization

Spin polarization is the degree to which the spin, i.e. the intrinsic angular momentum of elementary particles, is aligned with a given direction[1]. 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 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, thanks to the Curie law and it 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 semiconductors are being researched as possible spintronics materials.

The spin of free electrons is measured either by a LEED image from a clean wolfram-crystal (SPLEED)[2][3][4] 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.

References

  1. ^ J. Kessler (1976). Polarized Electrons. Springer Verlag Berlin Heidelberg. pp. 7–19. 
  2. ^ J. Kirschner and R. Feder (1979). "Spin Polarization in Double Diffraction of Low-Energy Electrons from W(001): Experiment and Theory". Physical Review Letters 42: 1008–1011. 
  3. ^ M. Kalisvaart, M. R. O'Neill, T. W. Riddle, F. B. Dunning, and G. K. Walters (1977). "Electron-spin polarization in low-energy electron diffraction from tungsten (001)". Physical Review B 17: 1570–1578. 
  4. ^ R. Feder (1976). "Spin Polarization in Low-Energy Electron Diffraction from W(001)". Physical Review Letters 36: 598–600. 

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