Spin Resolved Soft X-Ray Appearance Potential Spectroscopy

Abstract

A solution of the longstanding and persisting problem of band ferromagnetism will finally emerge from an understanding of the spindependent electronic structure of ferromagnetic materials¹. The prominent difficulty on this way is the rather small energy associated with magnetic ordering which is of the order of KT_c where T_c is the materials Curie temperature. This amount of energy is smaller or at most comparable to the presently achievable precision of band structure theory. The difficulties on the theoretical side have an experimental counterpart, namely the complexity added to standard band structure techniques by the necessity of analysis or proper preparation of electron spin. In fact the limited resolving power of spin detectors and the finite degrees of polarization of electron beams, usually only a fraction of the ideal 100%, enlarge the times for data aquisition sometimes to a prohibitive limit. Consider for example a quantity S which responds with S⁺ and S^- counts respectively to a number of N of 100% positively and negatively spin polarized electrons. For the much more realistic situation that only a beam of say p, typically 30%, spin polarization is available one would need at least N/p² electrons in order to determine S⁺ and S^- with the previous relative precision. Theoretical and experimental approaches to the problem of band ferromagnetism will therefore remain a tedious job.