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

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.