Correction to: Nature Materials https://doi.org/10.1038/s41563-019-0365-9, published online 13 May 2019.

In the version of this Comment originally published, \({\sqrt {{N}{\delta _{\mathrm{L}}}}}\) in the section ‘The challenge of d0 magnetism’ was incorrect; it should have said \({\sqrt {N}}{\delta _{\mathrm{L}}}\). This has been corrected in all versions of the Comment.