Since the discovery of the anomalous Hall effect (AHE), the anomalous Hall conductivity (AHC) has been thought to be zero when there is no net magnetization. However, the recently found relation between the intrinsic AHE and the Berry curvature predicts other possibilities, such as a large AHC in non-colinear antiferromagnets with no net magnetization but net Berry curvature.Vice versa, the AHE in principle could be tuned to zero, irrespective of a finite magnetization.Here, we experimentally investigate this possibility and demonstrate that, the symmetry elements of Heusler magnets can be changed such that the Berry curvature and all the associated properties are switched while leaving the magnetization unaffected. This enables us to tune the AHC from 0 Ω -1 cm -1 up to 1600 Ω -1 cm -1 with an exceptionally high anomalous Hall angle up to 12%, while keeping the magnetization same. Our study shows that the AHC can be controlled by selectively changing the Berry curvature distribution, independent of the magnetization. † Metallographic Characterization:The metallographic analysis was performed using an optical (Fig. S1) and a scanning probe electron (Fig. S2) microscopy for all the single crystals of Co2VGa (a), Co2MnGa (b) and Mn2CoGa (c). The samples are found to be single phase with homogeneous distribution of the chemical composition. The results of the compositional analysis with energy-dispersive X-ray (EDX) spectroscopy is summarized in table-S1. For the optical microscopy measurement, small crystals were embedded in epoxy resin blocks, and a smooth surface was prepared. In order to resolve the discrepancy between the theoretical calculation and the experimental Hall conductivity of the inverse Heusler compound Mn2CoGa, a detailed chemical analysis was performed. The chemical composition of the grown Mn2CoGa single crystals was determined as: Mn2.07Co1.04Ga confirming slight electron doping in the samples.

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We investigate the structural stability and magnetic properties of the cubic, tetragonal and hexagonal phases of Mn3Z (Z=Ga, Sn and Ge) Heusler compounds using first-principles density-functional theory. We propose that the cubic phase plays an important role as an intermediate state in the phase transition from the hexagonal to the tetragonal phases. Consequently, Mn3Ga and Mn3Ge behave differently from Mn3Sn, because the relative energies of the cubic and hexagonal phases are different. This result agrees with experimental observations for these three compounds. The weak ferromagnetism of the hexagonal phase and the perpendicular magnetocrystalline anisotropy of the tetragonal phase obtained in our calculations are also consistent with experiment.

We present a systematic study of transport and thermodynamic properties of the Laves phase system Nb 1−y Fe 2+y . Our measurements confirm that Fe-rich samples, as well as those rich in Nb ͑for ͉y͉ Ն 0.02͒, show bulk ferromagnetism at low temperature. For stoichiometric NbFe 2 , on the other hand, magnetization, magnetic susceptibility, and magnetoresistance results point toward spin-density wave ͑SDW͒ order, possibly helical, with a small ordering wave vector Q ϳ 0.05 Å −1 . Our results suggest that on approaching the stoichiometric composition from the iron-rich side, ferromagnetism changes into long-wavelength SDW order. In this scenario, Q changes continuously from 0 to small, finite values at a Lifshitz point in the phase diagram, which is located near y = +0.02. Further reducing the Fe content suppresses the SDW transition temperature, which extrapolates to zero at y Ϸ −0.015. Around this Fe content magnetic fluctuations dominate the temperature dependence of the resistivity and of the heat capacity which deviate from their conventional Fermi-liquid forms, inferring the presence of a quantum critical point. Because the critical point is located between the SDW phase associated with stoichiometric NbFe 2 and the ferromagnetic order which reemerges for very Nb-rich NbFe 2 , the observed temperature dependences could be attributed both to proximity to SDW order or to ferromagnetism.

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