4 - LS Coupling Basis for Magnetic Neutron Scatter

Abstract

The atomic electron environment, which causes magnetic scattering of neutrons, is covered in this chapter. In particular, the LS coupling mechanism, which is the result of the summing orbital angular momentum and spin momentum of the unpaired, atomic electrons, is presented. Also discussed are the spin and orbital angular momentum in the two-, three-, and the N -electron atoms followed by a discussion of LS coupling and the Pauli exclusion principle. The two-electron atom total wave function, which is described by either (1) symmetric spatial and antisymmetric spin components or (2) antisymmetric spatial and symmetric spin components is discussed. Then an N -electron system, which is described by the antisymmetric total eigenfunction expressed by Slater determinant, is described. Next, the Thomas precession factor for LS coupling as well as an alternative derivation for Thomas precession are derived. Finally, the quenching of electron orbital momentum in a crystal and an introduction to paramagnetic and ferromagnetic materials are discussed.