Large spin relaxation rates in trapped submerged-shell atoms

Spin relaxation due to atom-atom collisions is measured for magnetically trapped erbium and thulium atoms at a temperature near 500 mK. The rate constants for Er-Er and Tm-Tm collisions are 3.0 x 10(-10) and 1.1 x 10(-10) cm(3) s(-1), respectively, 2-3 orders of magnitude larger than those observed for highly magnetic S-state atoms. This is strong evidence for an additional, dominant, spin relaxation mechanism, electronic interaction anisotropy, in collisions between these submerged-shell, L not equal 0 atoms. These large spin relaxation rates imply that evaporative cooling of these atoms in a magnetic trap will be highly inefficient.