Towards ferromagnetic quantum criticality in FeGa3-xGex: 71Ga NQR as a zero field microscopic probe

TL;DR

This study investigates the evolution of ferromagnetic quantum criticality in FeGa3-xGex using 71Ga NQR, revealing a crossover from insulator to metal and evidence of 3D quantum critical fluctuations near the ferromagnetic threshold.

Contribution

It provides microscopic NQR evidence of quantum critical ferromagnetic fluctuations and the evolution of electronic states in Ge-doped FeGa3.

Findings

Observation of a crossover from insulator to correlated metal.

Detection of T4/3 power law indicating 3D quantum critical fluctuations.

Heavy electron behavior near the critical doping level.

Abstract

71Ga NQR, magnetization and specific heat measurements have been performed on polycrystalline Ge doped FeGa3 samples. A crossover from an insulator to a correlated local moment metal in the low doping regime and the evolution of itinerant ferromagnet upon further doping is found. For the nearly critical concentration at the threshold of ferromagnetic order, xC=0.15, (1/T1T) exhibits a pronounced T4/3 power law over two orders of magnitude in temperature which indicates 3D quantum critical ferromagnetic fluctuations. Furthermore, for the ordered x = 0.2 sample (TC = 6 K) 1/T1T could be fitted well in the frame of Moriya's SCR theory for weakly FM systems with 1/T1T proportional to chi. In contrast to this, the low doping regime nicely displays local moment behavior where 1/T1T proportional to chi2 is valid. For temperature tending to zero the Sommerfeld ratio = (C/T) is enhanced (70 mJ/mole-K2 for x = 0.1) which indicates the formation of heavy 3d-electrons.