Strength and scales of itinerant spin fluctuations in 3d paramagnetic metals

TL;DR

This paper investigates the spin density fluctuations in 3d paramagnetic metals using first-principles calculations, revealing their complex mixed character and significant on-site spin correlator despite the absence of local moments.

Contribution

The study provides a comprehensive first-principles analysis of spin density fluctuations, highlighting their mixed collective and single-particle nature across the entire Brillouin zone.

Findings

SDF have a mixed collective and single-particle character

Large on-site spin correlator results in effective fluctuating moments

SDF span wide energy and wavevector ranges, up to femtosecond scales

Abstract

The full spin density fluctuations (SDF) spectra in 3d paramagnetic metals are analyzed from first principles using the linear response technique. Using the calculated complete wavevector and energy dependence of the dynamic spin susceptibility, we obtain the most important, but elusive, characteristic of SDF in solids: on-site spin correlator (SC). We demonstrate that the SDF have a mixed character consisting of interacting collective and single-particle excitations of similar strength spreading continuously over the entire Brillouin zone and a wide energy range up to femtosecond time scales. These excitations cannot be adiabatically separated and their intrinsically multiscale nature should be always taken into account for a proper description of metallic systems. Overall, in all studied systems, despite the lack of local moment, we found a very large SC resulting in an effective fluctuating moment of the order of several Bohr magnetons.