Coherent spin valve phenomena and electrical spin injection in ferromagnetic/semiconductor/ferromagnetic junctions

TL;DR

This paper investigates quantum coherence effects in ferromagnetic/semiconductor/ferromagnetic junctions, revealing phenomena like quantum spin-valve effects that challenge classical spintronics assumptions, with implications for spin-injection analysis.

Contribution

It introduces a theoretical framework for quantum spin transport in ballistic ferromagnetic/semiconductor/ferromagnetic junctions, highlighting novel effects absent in classical models.

Findings

Quantum spin-valve effect occurs without net spin-polarized current.

Zero spin-valve signal can coexist with non-zero spin-current.

Temperature affects quantum spin-valve signatures but not their converse.

Abstract

Coherent quantum transport in ferromagnetic/ semiconductor/ ferromagnetic junctions is studied theoretically within the Landauer framework of ballistic transport. We show that quantum coherence can have unexpected implications for spin injection and that some intuitive spintronic concepts which are founded in semi-classical physics no longer apply: A quantum spin-valve (QSV) effect occurs even in the absence of a net spin polarized current flowing through the device, unlike in the classical regime. The converse effect also arises, i.e. a zero spin-valve signal for a non-vanishing spin-current. We introduce new criteria useful for analyzing quantum and classical spin transport phenomena and the relationships between them. The effects on QSV behavior of spin-dependent electron transmission at the interfaces, interface Schottky barriers, Rashba spin-orbit coupling and temperature, are systematically investigated. While the signature of the QSV is found to be sensitive to temperature, interestingly, that of its converse is not. We argue that the QSV phenomenon can have important implications for the interpretation of spin-injection in quantum spintronic experiments with spin-valve geometries.