Ordinary and intrinsic anomalous Hall effects in Nb1−yFe2+y

Abstract

The Hall effect of the dilution series Nb${}_{1\ensuremath{-}y}$Fe${}_{2+y}$ has been studied on selected samples spanning ferromagnetic (FM) and spin-density-wave (SDW) ground states, including a sample in the vicinity of the quantum critical point. Ordinary and anomalous contributions are observed, with positive ordinary Hall effect for all single crystals dominating at high temperatures. Consistent analysis of the anomalous contribution is possible for iron-rich Nb${}_{0.985}$Fe${}_{2.015}$ with ferromagnetic ground state and a SDW state at elevated temperatures and stoichiometric NbFe${}_{2}$ with a SDW ground state. The anomalous Hall coefficient is consistent with an intrinsic (Berry-phase) contribution, which is constant below the ordering temperature ${T}_{N}$ and gradually vanishes above ${T}_{N}$. The ordinary Hall coefficient is positive at all temperatures with a moderate temperature dependence. For stoichiometric NbFe${}_{2}$ and niobium-rich Nb${}_{1.01}$Fe${}_{1.99}$---both having a SDW ground state---an additional contribution to the Hall resistivity impedes a complete analysis and indicates the need for more sophisticated models of the anomalous Hall effect in itinerant antiferromagnets.