Control via electron count of the competition between magnetism and superconductivity in cobalt and nickel doped NaFeAs

TL;DR

This study demonstrates how electron doping via Co and Ni substitution in NaFeAs tunes the material from magnetic order to superconductivity, highlighting electron count as the key factor influencing this transition.

Contribution

It reveals that electron count, rather than dopant type, primarily controls the magnetic and superconducting states in NaFeAs, with Ni having twice the effect of Co at the same doping level.

Findings

Ni doping has double the effect of Co doping on superconductivity.

Superconductivity emerges after adding 0.1 electrons per Fe.

Magnetic order coexists with superconductivity at low doping levels.

Abstract

Using a combination of neutron, muon and synchrotron techniques we show how the magnetic state in NaFeAs can be tuned into superconductivity by replacing Fe by either Co or Ni. Electron count is the dominant factor, since Ni-doping has double the effect of Co-doping for the same doping level. We follow the structural, magnetic and superconducting properties as a function of doping to show how the superconducting state evolves, concluding that the addition of 0.1 electrons per Fe atom is sufficient to traverse the superconducting domain, and that magnetic order coexists with superconductivity at doping levels less than 0.025 electrons per Fe atom.