Spin-filtering efficiency of ferrimagnetic spinels CoFe2O4 and NiFe2O4

TL;DR

This study investigates the spin-filtering capabilities of CoFe2O4 and NiFe2O4 ferrimagnetic spinels in magnetic tunnel junctions, revealing that their efficiency depends on band alignment and wave-function symmetry, with potential for both positive and negative effects.

Contribution

It provides a detailed first-principles analysis showing that spin-filtering efficiency in these materials is highly sensitive to electronic structure details and band alignment.

Findings

Negative spin-filter effect suggested by density of states

Both positive and negative efficiencies are possible

Efficiency depends on band alignment and wave-function symmetry

Abstract

We assess the potential of the ferrimagnetic spinel ferrites CoFe2O4 and NiFe2O4 to act as spin filtering barriers in magnetic tunnel junctions. Our study is based on the electronic structure calculated by means of first-principles density functional theory within different approximations for the exchange correlation energy. We show that, in agreement with previous calculations, the densities of states suggest a lower tunneling barrier for minority spin electrons, and thus a negative spin-filter effect. However, a more detailed analysis based on the complex band-structure reveals that both signs for the spin-filtering efficiency are possible, depending on the band alignment between the electrode and the barrier materials and depending on the specific wave-function symmetry of the relevant bands within the electrode.