Magnetic diffusivity (${\eta }_m=1/({\mu }_0\sigma )$)

Magnetic diffusivity is the coefficient of magnetic diffusion. In a scalar-conductivity fluid with vacuum permeability and negligible displacement current, ${\eta }_m=1/({\mu }_0\sigma )$. Its dimensions are length squared per time, and a diffusion time on scale $L$ is $L^2/{\eta }_m$.