Zeeman Relaxation of Cold Atomic Iron and Nickel in Collisions with 3He

TL;DR

This study measures the ratio of diffusion to spin relaxation cross-sections in cold Fe-3He and Ni-3He collisions, revealing insights into Zeeman state dynamics and spin relaxation suppression in transition metals at cryogenic temperatures.

Contribution

Introduces a thermal excitation-inclusive model for Zeeman state decay, providing accurate cross-section ratios for Fe-3He and Ni-3He collisions at cryogenic temperatures.

Findings

Ni-3He cross-section ratio: 5 x 10^3

Fe-3He cross-section ratio: <= 3 x 10^3

Thermal excitations significantly affect Zeeman decay measurements

Abstract

We have measured the ratio of the diffusion cross-section to the angular momentum reorientation cross-section in the colliding Fe-3He and Ni-3He systems. Nickel (Ni) and iron (Fe) atoms are introduced via laser ablation into a cryogenically cooled experimental cell containing cold (< 1 K) 3He buffer gas. Elastic collisions rapidly cool the translational temperature of the ablated atoms to the helium temperature. The cross-section ratio is extracted by measuring the decays of the atomic Zeeman sublevels. For our experimental conditions, thermal energy is comparable to the Zeeman splitting. As a result, thermal excitations between Zeeman sublevels significantly impact the observed decay. To determine the cross-section ratio accurately, we introduce a model of Zeeman state dynamics that includes thermal excitations. We find the cross-section ratio for Ni-3He = 5 x 10^3 and Fe-3He <= 3 x 10^3 at 0.75 K in a 0.8 T magnetic field. These measurements are interpreted in the context of submerged shell suppression of spin relaxation as studied previously in transition metals and rare earth atoms.