Efficient Spin Transitions in Inelastic Electron Tunneling Spectroscopy

The excitation of the spin degrees of freedom of an adsorbed atom by tunneling electrons is computed using strong coupling theory. Recent measurements [Heinrich et al., Science 306, 466 (2004)] reveal that electron currents in a magnetic system efficiently excite its magnetic moments. Our theory shows that the incoming electron spin strongly couples with that of the adsorbate so that memory of the initial spin state is lost, leading to large excitation efficiencies. First-principles transmissions are evaluated in quantitative agreement with the experiment.

Figure 1

Electron transmission as a function of electron energy, $\omega$, between an STM tip (an atomic apex on a Cu(100) surface) and a Fe (lower panel) a Mn (upper panel) atom on a CuN monolayer on a Cu(100) electrode. The magnetic atom-apex distance is 5.2 Å in the present calculation. Full line: majority spin and dashed line: minority spin. The applied bias is zero. The wiggles in the transmission are due to the numerical discretization of the continuum states, the transmissions are thoroughly converged as checked by a fourfold increase of the density of states in the Fe case.

Figure 2

Computed conductance for a Fe atom on a CuN monolayer on Cu(100) in conductance quanta ($G_0=2e^2/h$). The conductances for increasing magnetic field $B$ are vertically displaced for representation purposes. The $B$ field is oriented along the $N$ axis in part (a) see scheme where $N$ atoms are represented by the small dark circles and the impurity by the red large one, and along the hollow axis on the surface in part (b), following the corresponding scheme.

Figure 3

Relative inelastic step heights in the conductance for Mn and Fe adsorbates as a function of the applied magnetic field, $B$, (along the $N$ axis): calculations (full lines) and experiment [3, 12] (symbols).