Chemically Mediated Quantum Criticality in NbFe2
Laves-phase Nb1+cFe2−c is a rare itinerant intermetallic compound exhibiting magnetic quantum criticality at ccr∼1.5%Nb excess; its origin, and how alloying mediates it, remains an enigma. For NbFe2, we show that an unconventional band critical point above the Fermi level EF explains most observations and that chemical alloying mediates access to this unconventional band critical point by an increase in EF with decreasing electrons (increasing %Nb), counter to rigid-band concepts. We calculate that EF enters the unconventional band critical point region for ccr>1.5%Nb and by 1.74%Nb there is no Nb site-occupation preference between symmetry-distinct Fe sites, i.e., no electron-hopping disorder, making resistivity near constant as observed. At larger Nb (Fe) excess, the ferromagnetic Stoner criterion is satisfied.
This article is from Phys. Rev. Lett. 107, 206401 (2011), doi:10.1103/PhysRevLett.107.206401. Posted with permission.