Doping-driven magnetic instabilities and quantum criticality ofNbFe2

Abstract

Using density functional theory we investigate the evolution of the magnetic ground state of NbFe2 due to doping by Nb-excess and Fe-excess. We find that non-rigid-band effects, due to the contribution of Fe-d states to the density of states at the Fermi level are crucial to the evolution of the magnetic phase diagram. Furthermore, the influence of disorder is important to the development of ferromagnetism upon Nb doping. These findings give a framework in which to understand the evolution of the magnetic ground state in the temperature-doping phase diagram. We investigate the magnetic instabilities in NbFe2. We find that explicit calculation of the Lindhard function, χ0(q), indicates that the primary instability is to finite q antiferromagnetism driven by Fermi surface nesting. Total energy calculations indicate that q = 0 antiferromagnetism is the ground state. We discuss the influence of competing q = 0 and finite q instabilities on the presence of the non-Fermi liquid behavior in this material.

Metallic quantum ferromagnets

“…19). The fact that both iron and niobium-rich samples are FM at low temperature has been linked to the peculiar electronic structure of this material (Alam and Johnson, 2011;Neal et al, 2011;Subedi and Singh, 2010;Tompsett et al, 2010). Part of the phase diagram can also be reproduced by applying hydrostatic pressure : Starting with a FM sample with y = 0.015, increasing pressure is equivalent to moving the system to the left in the phase diagram of Fig.…”

Quantum criticality in NbFe2induced by zero carrier velocity

“…26 The point we will emphasize here is the wiggle in the band just crossing E F along the Γ-M direction that produces an unusually flat portion only 6 meV (equivalent to 70 K temperature) above E F . We argue that, when the Fermi level is tuned to this critical point, the vanishing velocity in this critical region produces unusual low energy electronic excitations that can account for anomalous behavior, viz.…”

Chemically Mediated Quantum Criticality inNbFe2

“…Of course, including properly the effects of disorder in these class of systems, specifically at such a small doping (c), is a considerable challenge. Attempting to address doping, recent studies use the virtual crystal approximation 10 (VCA) or supercells (ordered array of dopants), 11 having severe shortcomings, as we discuss.…”