Magnetic Relaxation in Dysprosium-dysprosium Collisions

Abstract

The collisional magnetic reorientation rate constant (\vartheta_{\mathbb{R}}) is measured for magnetically trapped atomic dysprosium (Dy), an atom with large magnetic dipole moments. Using buffer gas cooling with cold helium, large numbers (>10(^{11})) of Dy are loaded into a magnetic trap and the buffer gas is subsequently removed. The decay of the trapped sample is governed by collisional reorientation of the atomic magnetic moments. We find (\vartheta_{\mathbb{R}} = 1.9 \pm 0.5 \times 10^{-11} , \text{cm}^{3} , \text{s}^{-1}) at 390 mK. We also measure the magnetic reorientation rate constant of holmium (Ho), another highly magnetic atom, and find (\vartheta_{\mathbb{R}} = 5 \pm 2 \times 10^{-12} , \text{cm}^3, \text{s}^{-1}) at 690 mK. The Zeeman relaxation rates of these atoms are greater than expected for the magnetic dipole-dipole interaction, suggesting that another mechanism, such as an anisotropic electrostatic interaction, is responsible. Comparison with estimated elastic collision rates suggests that Dy is a poor candidate for evaporative cooling in a magnetic trap.