Theory of Inelastic Electron Tunneling from a Localized Spin in the   Impulsive Approximation
  A simple expression for the conductance steps in the inelastic electron tunneling from spin excitations in a single magnetic atom adsorbed on a non-magnetic metal surfaces is derived. The inelastic coupling between the tunneling electron and the spin is via the exchange coupling and is treated in an impulsive approximation using the Tersoff-Hamann approximation for the tunneling between the tip and the sample. Our results for conductance steps justify the analysis carried out by Hirjebedin et al. [Science 317, 1199 (2007)] of observed step-like conductances by inelastic electron tunneling from spin excitations in a single magnetic adatom using a simple spin matrix element. In addition, our result gives a simple expression for the magnitudes of conductance steps and their lateral spatial variation with respect to the tip position, which can be calculated directly from spin-polarized wave functions at the Fermi level of the sample. 
Mats Persson