How reliable are Hanle measurements in metals in a three-terminal geometry?

TL;DR

This paper critically examines the reliability of Hanle measurements in metals using three-terminal devices, revealing significant discrepancies with standard theory and suggesting the signals originate from the tunnel junction rather than spin accumulation.

Contribution

The study demonstrates that Hanle signals in three-terminal measurements are often not due to spin accumulation, challenging the validity of this method for measuring spin properties in metals.

Findings

Hanle signals are 8 orders of magnitude larger than predicted.

Temperature and voltage dependence do not match spin polarization.

Signals scale with interface resistance, indicating origin in tunnel junction.

Abstract

We test the validity of Hanle measurements in three-terminal devices by using aluminum (Al) and gold (Au). The obtained Hanle and inverted Hanle-like curves show an anomalous behavior. First, we measure Hanle signals 8 orders of magnitude larger than those predicted by standard theory. Second, the temperature and voltage dependences of the signal do not match with the tunneling spin polarization of the ferromagnetic contact. Finally, the spin relaxation times obtained with this method are independent of the choice of the metallic channel. These results are not compatible with spin accumulation in the metal. Furthermore, a scaling of the Hanle signal with the interface resistance of the devices suggests that the measured signal is originated in the tunnel junction.