From mean-field localized magnetism to itinerant spin fluctuations in the "Non-metallic metal" - FeCrAs

TL;DR

FeCrAs exhibits a unique magnetic behavior with high-energy spin fluctuations that likely cause its unusual electrical properties, bridging localized and itinerant magnetism concepts.

Contribution

This study provides the first neutron scattering analysis revealing the coexistence of magnetic order and high-energy spin fluctuations in FeCrAs.

Findings

Cr3+ magnetic order at 115 K with mean-field critical exponent

Gapless magnetic fluctuations observed up to 80 meV

High-energy spin fluctuations resemble itinerant magnetism

Abstract

FeCrAs displays an unusual electrical response that is neither metallic in character nor divergent at low temperatures, as expected for an insulating response, and therefore it has been termed a "nonmetal-metal". We carried out neutron scattering experiments on powder and single crystal samples to study the magnetic dynamics and critical fluctuations in FeCrAs. Magnetic neutron diffraction measurements find Cr3+ magnetic order setting in at 115 K with the mean-field critical exponent. Neutron spectroscopy, however, observes gapless stiff magnetic fluctuations emanating from magnetic positions with propagation wave vector q_0=(1/3,1/3), which persists up to at least 80 meV. The magnetism in FeCrAs therefore displays a response which resembles that of itinerant magnets at high energy transfers, such as chromium alloys. We suggest that the presence of stiff high-energy spin fluctuations is the origin of the unusual temperature dependence of the resistivity.