Large spin accumulation voltages in epitaxial Mn5Ge3 contacts on Ge without oxide tunnel barrier

TL;DR

This study demonstrates large spin accumulation voltages in epitaxial Mn5Ge3 contacts on germanium without using an oxide tunnel barrier, revealing unexpected magnitudes likely originating from the germanium itself.

Contribution

It reports the observation of unexpectedly large spin voltages in Mn5Ge3/Ge contacts without oxide barriers, challenging existing spin injection theories.

Findings

Spin voltages are several orders of magnitude larger than theoretical predictions.

Clear Hanle and inverted Hanle signals observed up to 200 K.

Discrepancy suggests spin accumulation originates from Ge bulk or depletion region.

Abstract

Spin injection in high-quality epitaxial Mn5Ge3 Schottky contacts on n-type Ge has been investigated using a three-terminal Hanle effect measurement. Clear Hanle and inverted Hanle signals with features characteristic of spin accumulation and spin precession are observed up to 200 K. Strikingly, the observed spin voltage is several orders of magnitude larger than predicted by the theory of spin injection and diffusive spin transport. Since the devices have no oxide tunnel barrier, the discrepancy between theory and experiments cannot be explained by the often-invoked spin accumulation in localized states associated with the oxide or oxide/semiconductor interface. The observed spin voltages therefore must originate from the Ge itself, either from spins in the Ge bulk bands or its depletion region.