Spin Wave Dispersion on the Nanometer Scale

Hot electrons injected into antiferromagnetic Mn layers from the tip of a low temperature scanning tunneling microscope have been used to determine the energies, lifetimes, and momenta of antiferromagnetic spin waves on the nanometer scale. The spin waves show a linear dispersion with a velocity of $160\pm 10\mathrm{meV}\AA$ and lifetimes that scale linearly with energy in agreement with neutron scattering and theory. It is shown that the method is sensitive enough to detect the influence of surface anisotropies on the spin wave dispersion.

Figure 1

Topographies of (a) 5.8 ML and (b) 24 ML Mn on ${\mathrm{Cu}}_3\mathrm{Au}(001)$.

Figure 2

$d^{2}I/d{U}^2$ spectra of various thicknesses Mn thin films on ${\mathrm{Cu}}_3\mathrm{Au}(001)$. The zero order (cross), first order (circle), and second order (parallelogram) excitation peaks are marked in the figure. These excitations correspond to standing spin waves as sketched in the inset.

Figure 3

Spin wave dispersion of $\gamma$-Mn. The notations (cross, circle, parallelogram) of STM data are the same as in Fig. 2. The extrapolated neutron scattering data is from 18. The fcc and fct Mn dispersions were obtained by ab initio calculations. The upper inset gives the gap $E_g$ as a function of film thickness (see text) and the lower, the FWHM as a function of $k$.