Thermal neutron scattering by magnetic interaction

Scattering of thermal neutrons on crystals is a powerful technique to study microscopic properties of condensed matter. The present article is confined to magnetic interaction through the magnetic dipole of the neutron with the magnetic dipoles of the atoms due to unpaired electrons. The general theory of scattering by magnetic interaction is presented. Further consideration is given to the properties of a three dimensionally ordered lattice leading to diffraction maxima described by Bragg’s law. The interpretation of diffraction diagrams is discussed with special attention given to helical spin configurations. Covalency of the chemical bond can be investigated by neutron diffraction and its consequences on the diffraction properties are discussed. The neutron magnetic moment comes about because of the neutron having spin [math], which can be in the two states +[math] or —[math]. This leads to the possibility of generating polarized beams with all neutrons in one spin state. The polarized beam technique is treated as a special and powerful tool for studying microscopic magnetic properties of condensed matter and especially of spin densities in crystals. The polarization analysis of the diffracted beam in a polarized beam experiment is a logic consequence and adds a new dimension to the investigation, which enables one to study further details and to separate magnetic and nuclear interactions, order and disorder properties of the crystal