Evolution of magnetic fluctuations through the Fe-induced paramagnetic to ferromagnetic transition in Cr$_2$B

TL;DR

This study investigates how Fe doping influences magnetic fluctuations and phase transitions in Cr$_2$B, revealing the suppression of antiferromagnetic fluctuations and the emergence of ferromagnetism near a quantum critical point.

Contribution

It provides new insights into the evolution of magnetic fluctuations and the nature of quantum phase transitions in Fe-doped Cr$_2$B, highlighting the effects of quenched disorder.

Findings

Suppression of antiferromagnetic fluctuations with Fe doping

Emergence of ferromagnetism beyond critical doping level

Presence of non-Fermi liquid behavior near the quantum critical point

Abstract

In itinerant ferromagnets, the quenched disorder is predicted to dramatically affect the ferromagnetic to paramagnetic quantum phase transition driven by external control parameters at zero temperature. Here we report a study on Fe-doped Cr$_2$B, which, starting from the paramagnetic parent, orders ferromagnetically for Fe-doping concentrations $x$ larger than $x_{\rm c}=2.5$\%. In parent Cr$_2$B, $^{11}$B nuclear magnetic resonance data reveal the presence of both ferromagnetic and antiferromagnetic fluctuations. The latter are suppressed with Fe-doping, before the ferromagnetic ones finally prevail for $x>x_{\rm c}$. Indications for non-Fermi liquid behavior, usually associated with the proximity of a quantum critical point, were found for all samples, including undoped Cr$_2$B. The sharpness of the ferromagnetic-like transition changes on moving away from $x_{\rm c}$, indicating significant changes in the nature of the magnetic transitions in the vicinity of the quantum critical point. Our data provide constraints for understanding quantum phase transitions in itinerant ferromagnets in the limit of weak quenched disorder.