Spin polarization
[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.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.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.