Ferromagnetic Quantum Critical Point in Heavy-Fermion Iron Oxypnictide Ce(Ru$_{1-x}$Fe$_x$)PO

TL;DR

This study investigates ferromagnetic quantum criticality in Ce(Ru_{1-x}Fe_{x})PO using NMR, revealing a quantum critical point near x=0.86 where ferromagnetic order vanishes, providing a new platform for studying heavy-fermion quantum criticality.

Contribution

It identifies a ferromagnetic quantum critical point in Ce(Ru_{1-x}Fe_{x})PO, a rare example among itinerant ferromagnets, and compares its critical behavior to YbRh_{2}Si_{2}.

Findings

Critical fluctuations observed down to 0.3 K near x=0.86.

Continuous suppression of Curie temperature and moments with Fe substitution.

Similarity of critical behavior to YbRh_{2}Si_{2} indicating local f-electron criticality.

Abstract

We have performed ^{31}P-NMR measurements on Ce(Ru_{1-x}Fe_{x})PO in order to investigate ferromagnetic (FM) quantum criticality, since heavy-fermion (HF) ferromagnet CeRuPO with a two-dimensional structure turns to a HF paramagnet by an isovalent Fe-substitution for Ru. We found that Ce(Ru_{0.15}Fe_{0.85})PO shows critical fluctuations down to \sim 0.3 K, as well as the continuous suppression of Curie temperature and the ordered moments by the Fe-substitution. These experimental results suggest the presence of a FM quantum critical point (QCP) at x \sim 0.86, which is a rare example among itinerant ferromagnets. In addition, we point out that the critical behaviors in Ce(Ru_{0.15}Fe_{0.85})PO share the similarity with those in YbRh_{2}Si_{2}, where the local criticality of $f$ electrons has been discussed. We reveal that Ce(Ru_{1-x}Fe_{x})PO is a new system to study FM quantum criticality in HF compounds.