Measurements of spin diffusion length in gold with point contact Andreev reflection spectroscopy

Spin diffusion length, $L_{s}$, is of fundamental importance for spin dependent transport and spintronic devices. So far, most of the measurements of $L_{s}$ in non-magnetic metals have been done in the lateral non-local geometry, with the chemical potential difference characterizing the spin imbalance. In our approach the spin diffusion length was measured directly with point contact Andreev reflection spectroscopy. A spin polarized current was injected from a ferromagnetic electrode, Co$_{2}$Mn$_{0.5}$Fe$_{0.5}$Si Heulser alloy, into Au films of variable thickness. The spin current, which gradually decays with the increased thickness of the film, was measured with a superconducting Nb tip. We developed a phenomenological theory which allowed us to determine the values of $L_{s}$ in such a system. We found $L_{s}$ to be on the order of 250 nm at 4 K, comparable to the results obtained by other techniques. Similar results were obtained with a Gd single crystal.