Spin precession and inverted Hanle effect in a semiconductor near a finite-roughness ferromagnetic interface

TL;DR

This paper demonstrates that interface roughness-induced local magnetic fields significantly affect spin accumulation and dynamics in semiconductor/ferromagnet structures, impacting the interpretation of spin lifetime measurements.

Contribution

It reveals the dominant role of local magnetostatic fields from interface roughness in spin behavior, highlighting the need to consider these effects in spintronic experiments.

Findings

Spin precession reduces spin accumulation up to tenfold.

Inhomogeneous fields cause non-collinear spin orientations.

A new lower bound of 0.29 ns for spin lifetime in doped Si.

Abstract

Although the creation of spin polarization in various non-magnetic media via electrical spin injection from a ferromagnetic tunnel contact has been demonstrated, much of the basic behavior is heavily debated. It is reported here for semiconductor/Al2O3/ferromagnet tunnel structures based on Si or GaAs that local magnetostatic fields arising from interface roughness dramatically alter and even dominate the accumulation and dynamics of spins in the semiconductor. Spin precession in the inhomogeneous magnetic fields is shown to reduce the spin accumulation up to tenfold, and causes it to be inhomogeneous and non-collinear with the injector magnetization. The inverted Hanle effect serves as experimental signature. This interaction needs to be taken into account in the analysis of experimental data, particularly in extracting the spin lifetime and its variation with different parameters (temperature, doping concentration). It produces a broadening of the standard Hanle curve and thereby an apparent reduction of the spin lifetime. For heavily doped n-type Si at room temperature it is shown that the spin lifetime is larger than previously determined, and a new lower bound of 0.29 ns is obtained. The results are expected to be general and occur for spins near a magnetic interface not only in semiconductors but also in metals, organic and carbon-based materials including graphene, and in various spintronic device structures.