External magnetic field suppression of carbon diffusion in iron

TL;DR

This study uses DFT calculations to show how external magnetic fields suppress carbon diffusion in iron by altering electron density and atomic cages, revealing the underlying physical mechanism.

Contribution

It introduces a computational model that reproduces experimental suppression of carbon diffusion under magnetic fields and explains the physical mechanism behind it.

Findings

Magnetic fields reduce carbon diffusivity in iron.

Increasing magnetic disorder flattens the electron density of states.

Applied magnetic fields reverse the effects of magnetic disorder.

Abstract

External magnetic fields reduce diffusion of carbon in BCC iron, but the physical mechanism is not understood. Using DFT calculations with magnetic moments sampled from a Heisenberg model, we calculate diffusivities of carbon in iron at high temperatures and with field. Our model reproduces the measured suppression of diffusivity from field. We find that increasing magnetic disorder flattens the electron density of states compared with the ferromagnetic case, which distorts the octahedral cages around carbon, lowering the activation barrier to diffusion; an applied field reverses these trends.