Tunable anomalous Hall conductivity through volume-wise magnetic competition in a topological kagome magnet

Abstract

Magnetic topological phases of quantum matter are an emerging frontier in physics and material science [1][2][3][4]. Along these lines, several kagome magnets [5][6][7][8][9] have appeared as the most promising platforms. However, the magnetic nature of these materials in the presence of topological state remains an unsolved issue [5][6][7][8][9]. Here, we explore magnetic correlations in the kagome magnet Co 3 Sn 2 S 2 . Using muon spin-rotation, we present evidence for competing magnetic orders in the kagome lattice of this compound. Our results show that while the sample exhibits an outof-plane ferromagnetic ground state, an in-plane antiferromagnetic state appears at temperatures above 90 K, eventually attaining a volume fraction of 80% around 170 K, before reaching a nonmagnetic state. Strikingly, the reduction of the anomalous Hall conductivity above 90 K linearly follows the disappearance of the volume fraction of the ferromagnetic state. We further show that the competition of these magnetic phases is tunable through applying either an external magnetic field or hydrostatic pressure. Our results taken together suggest the thermal and quantum tuning of Berry curvature field via external tuning of magnetic order. Our study shows that Co 3 Sn 2 S 2 is a rare example where the magnetic competition drives the thermodynamic evolution * Electronic address: zurab.guguchia@psi.ch of the Berry curvature field, thus tuning its topological state.The kagome lattice is a two-dimensional pattern of corner-sharing triangles. With this unusual symmetry and the associated geometrical frustration, the kagome lattice can host peculiar states including flat bands [8], Dirac fermions [5,6] and spin liquid phases [7,10]. In particular, magnetic kagome materials offer a fertile ground to study emergent behaviors resulting from the interplay between unconventional magnetism and band topology. Recently, transition-metal based kagome magnets [5][6][7][8][9][10][11][12][13] are emerging as outstanding candidates for such studies, as they feature both large Berry curvature fields and unusual magnetic tunability. In this family, the kagome magnet Co 3 Sn 2 S 2 is found to exhibit both a large anomalous Hall effect and anomalous Hall angle, and is identified as a promising Weyl semimetal candidate [9,11,14,15]. However, despite knowing the magnetic ground state is ferromagnetic below T C = 177 K [16] with spins aligned along the c-axis [9, 11, 17] (see Figs. 1 a and b) there is no report of its magnetic tunability or phase diagram, and its interplay with the topological band structure. Here we use high-resolution µSR to systematically characterize the phase diagram, uncovering another intriguing in-plane antiferromagnetic phase. The magnetic competition between these two phases is further found to be highly tunable via applying either pressure [18][19][20][21] or magnetic field. Combined with first principles calculations, we discover that the tunable magnetic correlation plays a key role in determining the giant anomalous Hall transp...

Exchange biased anomalous Hall effect driven by frustration in a magnetic kagome lattice

“…A recent work using muon spin rotation [11] concluded that the magnetism in Co 3 Sn 2 S 2 originates solely from the Co atoms, and that there is a phase transition from a higher temperature in-plane AFM to a low temperature out-of-plane FM at ∼ 90 K. This is difficult to reconcile with our observations, since simple FM alone does not exhibit EB. To resolve this, we measured the magnetic moment of a Co 3 Sn 2 S 2 crystal as a function of temperature in both out-of-plane ( Fig.…”

“…The observation of AFM correlations in Ref. [11] using muon spectroscopy, may be consistent with this interpretation; the FM (with the moment predominantly aligned along c) onsets at T C , however frustrated in-plane AFM correlations cause weak in-plane canting, that subsequently freezes at T G into a dense SG. The coexistence of the spin glass and the FM phase then leads to exchange biased AHE presently observed.…”

“…The difficulty with reconciling an AFM coexistence at T G < T < T c , is that EB is not observed in this range, but rather at T < T G . This means that the coexisting phase must become stiffer below T G , not weaker as previously suggested [11]. However, the absence of a heat capacity anomaly at T G , suggests this does not freeze a significant fraction of the degrees of freedom, and in any case muon measurements have confirmed the absence of a competing long range order at low temperatures.…”

“…As a minimal Landau model, this can be understood as the interplay of two terms in the free energy, one favoring a FM structure M = ±M 0 , and another with a minimum favoring M = 0. This could be the coexistence of an AFM, as claimed recently [11], or a correlated paramagnet (PM) with AFM interactions.…”

33% Giant Anomalous Hall Current Driven by Both Intrinsic and Extrinsic Contributions in Magnetic Weyl Semimetal Co3Sn2S2

“…As the AHC at x = 0 is basically dominated by the Berry curvature of the topological band structures, the AHC remains unchanged below 100 K. [17] With further increase in temperature, the increase in thermal disturbance initiates the random arrangement of magnetic moments, which reduces the strength of the Berry curvature and AHC. [17,32,33] Above TC, the AHC disappears because the magnetic moment is completely disordered. For x = 0.025, 0.05, 0.10, 0.15, and 0.20, the AHC decreases with increase in temperature; this result is discussed later in the paper.…”