Quantum effects in atomically perfect specular spin valve structures

TL;DR

This paper presents a quantum-mechanical model for spin-dependent transport in highly coherent spin valve structures, showing that specularity can nearly maximize magnetoresistance independently of certain material parameters.

Contribution

It introduces a quantum model for spin transport in specular spin valves, highlighting the role of quantum coherence and state transformation in magnetoresistance enhancement.

Findings

Specularity can nearly reach 100% magnetoresistance.

Quantum coherence significantly influences spin transport.

Magnetoresistance is largely independent of carrier lifetime differences.

Abstract

A simple tight-binding theoretical model is proposed for spin dependent, current-in-plane transport in highly coherent spin valve structures under specularity conditions. Using quantum-mechanically coherent and spatially quantized Fermi states in the considered multilayered system, a system of partial Boltzmann kinetic equations is built for relevant subbands to yield the expressions for conductance in parallel or antiparallel spin valve states and thus for the magneto-conductance. It is shown that specularity favors the magnetoresistance to reach its theoretical maximum for this structure close to 100%. This result is practically independent of the model parameters, in particular it does not even need that lifetimes of majority and minority carriers be different (as necessary for the quasiclassical regimes). The main MR effect in the considered limit is due to the transformation of coherent quantum states, induced by the relative rotation of magnetization in the FM layers. Numerical calculation based on the specific Boltzmann equation with an account of spin-dependent specular reflection at the interfaces is also performed for a typical choice of material parameters.