Nonmagnetic-magnetic transition and magnetically ordered structure in SmS

TL;DR

This study reveals a magnetic transition in SmS under high pressure, characterized by a unique magnetic order that challenges conventional heavy fermion models, suggesting a complex antiferromagnetic structure.

Contribution

The paper provides the first high-pressure NMR evidence of a magnetic transition in SmS with a type II antiferromagnetic structure, beyond simple localized electron models.

Findings

Magnetic transition occurs above 2 GPa pressure.

Ordered phase exhibits a type II antiferromagnetic structure.

Localized 4f electrons are fully screened near transition.

Abstract

SmS, a prototypical intermediate valence compound, has been studied by performing high-pressure nuclear magnetic resonance measurements on a $^{33}$S-enriched sample. The observation of an additional signal below 15-20 K above a nonmagnetic-magnetic transition pressure $P_{\rm c2} \approx 2$ GPa gives evidence of a magnetic transition. The absence of a Curie-term in the Knight shift near $P_{\rm c2}$ indicates that the localized character of $4f$ electrons is entirely screened and the mechanism of the magnetic ordering is not described within a simple localized model. Simultaneously, the line shape in the magnetically ordered state is incompatible with a spin density wave order. These suggest that the magnetic order in SmS may require an understanding beyond the conventional framework for heavy fermions. The fact that hyperfine fields from the ordered moments cancel out at the S site leads us to a conclusion that the ordered phase has a type II antiferromagnetic structure.