Spin nomenclature for semiconductors and magnetic metals

The different conventions used in the semiconductor and magnetic metals communities can cause confusion in the context of spin polarization and transport in simple heterostructures. In semiconductors, terminology is based on the orientation of the electron spin, while in magnetic metals it is based on the orientation of the moment. In the rapidly expanding field of spintronics, where both semiconductors and metallic metals are important, some commonly used terms ("spin-up," "majority spin") can have different meanings. Here, we clarify nomenclature relevant to spin transport and optical polarization by relating the common physical observables and "definitions" of spin polarization to the fundamental concept of conservation of angular momentum within a well-defined reference frame.