Muon contact hyperfine field in metals: A DFT calculation

TL;DR

This paper evaluates the accuracy of DFT calculations for muon hyperfine contact fields in metals, including complex magnetic compounds, demonstrating improved agreement with experimental data through advanced computational methods.

Contribution

It introduces a systematic DFT approach using spin-polarized plane waves and the reduced Stoner theory to accurately estimate muon hyperfine fields in metals and magnetic compounds.

Findings

DFT estimates align well with experimental hyperfine fields in metals.

Inclusion of core state effects improves accuracy in magnetic materials.

Reduced Stoner theory enhances DFT predictions for itinerant magnets.

Abstract

In positive muon spin rotation and relaxation spectroscopy it is becoming nowadays customary to take advantage of Density Functional Theory (DFT) based computational methods to aid the experimental data analysis. DFT aided muon site determination is especially useful for measurements performed in magnetic materials, where large contact hyperfine interactions may arise. Here we present a systematic analysis of the accuracy of the ab initio estimation of muon's hyperfine contact field on elemental transition metals, performing state of the art spin-polarized plane wave DFT and using the projector augmented pseudopotential approach, which allows to include the core state effects due to the spin ordering. We further validate this method in not-so-simple, non-centrosymmetric metallic compounds, presently of topical interest for their spiral magnetic structure giving rise to skyrmion phases, such as MnSi and MnGe. The calculated hyperfine fields agree with experimental values in all cases, provided the spontaneous spin magnetization of the metal is well reproduced within the approach. To overcome the known limits of the conventional mean field approximation of DFT on itinerant magnets, we adopt the so-called reduced Stoner theory [L. Ortenzi et al.,Phys. Rev. B 86, 064437 (2012)]. We establish the accuracy of the estimated muon contact field in metallic compounds with DFT and our results show improved agreement with experiments compared to those of earlier publications.