How Stray Oxygen Scrambles Signals in Spintronics

For years, the performance of iron and magnesium oxide (Fe/MgO/Fe) magnetic tunnel junctions—crucial components in magnetic memory and sensors—has been stifled by a persistent foe: interfacial oxidisation. While engineers knew that stray oxygen atoms at the interface limited efficiency, a complete theoretical framework explaining the chaotic behaviour of electrons in these conditions remained elusive.

Now, researchers have developed an ab-initio quantum transport approach to solve this puzzle. By integrating a mathematical method known as 'vertex corrections' with the Coherent Potential Approximation, the team successfully modelled the substitutional disorder found at oxidised interfaces. Their findings are stark: oxidation does not merely dampen the signal; it fundamentally reshapes spin-dependent transport.

The study demonstrates that oxidation triggers 'incoherent scattering', where electrons are bounced off their intended path, creating disorder-assisted channels. This phenomenon suppresses the tunnel magnetoresistance (TMR) ratio—a key measure of efficiency—and can even reverse the signal at high voltages. Paradoxically, in highly oxidised junctions, increasing the thickness of the barrier actually degrades performance further, as these chaotic incoherent channels overwhelm the clean, coherent tunnelling current. This predictive framework proves that idealised models are no longer sufficient for designing realistic spintronic devices.