Enhanced Pauli spin response, failure of Stoner \& spin fluctuation models, and presence of 6 $eV$ plasmonic excitations in Ni metal

TL;DR

This study uses advanced theoretical methods to analyze Ni's electronic and magnetic properties, revealing deviations from standard models, significant spin susceptibility contributions, mixed valence states, non-Fermi-liquid behavior, and plasmonic excitations at 6 eV.

Contribution

It provides a comprehensive first-principles analysis of Ni's electronic structure, magnetism, and excitations, highlighting failures of traditional models and identifying plasmonic features.

Findings

Deviation from Stoner and spin fluctuation models in magnetization

Presence of mixed valence electronic configurations in Ni

Identification of 6 eV plasmonic excitations and satellite features

Abstract

We revisit the electronic structure of Ni, using the density functional theory (DFT) and dynamical mean-field theory (DMFT) for the theoretical description of its electronic structure properties along with finite-temperature magnetism. Our study provides a comprehensive account of electronic and magnetic properties with the same set of Coulomb interaction parameters, $U$($J$)=5.78(1.1) $eV$ calculated using first-principles approach. The nature of theoretical magnetization curves obtained from DFT \& DFT+DMFT as well as the experimental curve show deviation from the standard models of magnetism, $viz$ Stoner and spin fluctuation model. The temperature dependent DFT approach is found to well describe the finite-temperature M(T) of Ni below critical temperature ($T$ $\leq$ 631 K). The study finds significant Pauli-spin susceptibility contribution to paramagnetic spin susceptibility. Excluding the Pauli-spin response yields a linear Curie-Weiss dependence of the inverse paramagnetic susceptibility at higher temperatures. Also, the presence of mixed valence electronic configuration (3$d^8$, 3$d^9$ and 3$d^7$) is noted. The competing degrees of both the itinerant and localized moment picture of 3$d$ states are found to dictate the finite-temperature magnetization of the system. Furthermore, the quasiparticle scattering rate is found to exhibit strong deviation from $T^2$ behavior in temperature leading to the breakdown of conventional Fermi-liquid theory. In addition to the 6 $eV$ feature, our calculated electronic excitation spectrum confirms the satellite feature extending $\sim$10 $eV$ binding energy, being consistent with experimental observation. Interestingly, our $G_0W_0$ results find the presence of plasmonic excitation contribution to the intensity of famous 6 $eV$ satellite along with the electronic correlation effects,paving way for its reinterpretation.