Large Hall and Nernst responses from thermally induced spin chirality in a spin-trimer ferromagnet

Abstract

The long-range order of noncoplanar magnetic textures with scalar spin chirality (SSC) can couple to conduction electrons to produce an additional (termed geometrical or topological) Hall effect. One such example is the Hall effect in the skyrmion lattice state with quantized SSC. An alternative route to attain a finite SSC is via the spin canting caused by thermal fluctuations in the vicinity of the ferromagnetic ordering transition. Here, we report that for a highly conducting ferromagnet with a two-dimensional array of spin trimers, the thermally generated SSC can give rise to a gigantic geometrical Hall conductivity even larger than the intrinsic anomalous Hall conductivity of the ground state. We also demonstrate that the SSC induced by thermal fluctuations leads to a strong response in the Nernst effect. A comparison of the sign and magnitude of fluctuation–Nernst and Hall responses in fundamental units indicates the need for a momentum–space picture to model these thermally induced signals.

Highly anisotropic geometrical Hall effect via f-d exchange fields in doped pyrochlore molybdates

“…4 [100] gradually increases, reaches maximum at ∼ 8 µ B /f.u., and eventually decreases towards zero at the full moment of 15.5 µ B /f.u. We speculate that the envelope-shaped magnetization dependence, which is also observed in several materials [3,27], reflects the modulation of Tb magnetic states. Both Tb and Mo magnetic moments are disordered at zero magnetic field.…”

Kagome lattice promotes chiral spin fluctuations

“…ing beyond previous experimental reports focused on the phenomenological observation of this effect [15,17,[21][22][23], we provide an expanded view of spin chirality driven by thermal fluctuations, emphasizing the atomistic lattice as a key factor in its amplification or suppression.…”

“…The skyrmion lattice [26] In presence of singularities in the electronic structure of solids, e.g. in presence of Weyl-type monopoles or line degeneracies, the thermoelectric ratio is expected to approach the quantized value k B /e when the thermal energy k B T is larger than disorder-induced level broadening h/τ with carrier lifetime τ [17,[42][43][44]. We report a notable suppression of the thermoelectric ratio to 0.04 in the skyrmion lattice phases of both compounds, where the heat bath temperature is far below h/τ ∼ 70 Kelvin, estimated in Extended Note 3.…”

“…Recent theories emphasize rectification processes facilitated by transient spin arrangements: during their rapid movement on the time-scale of picoseconds, clusters of thermally agitated spins on lattice sites i, j, k are endowed with a local scalar spin chirality, mathematically described as χ = S i • (S j × S k ), whose thermal average χ T , referred to by the shorthand SSC in the following, can be constant in time despite absence of long-range order [4,5,15,16]. The development of design principles for materials with fluctuation-driven SSC, particularly as related to exploitation of common lattice motifs, promises new impulses for controlling heat and charge transport [4,5,15,17], magneto-optical responses [18,19], and the second harmonic generation of light [20]. Mov- *…”

Spin-Chirality-Driven Quantum Anomalous and Quantum Topological Hall Effects in Chiral Magnets

“…61 The vector-spin structures for kagome chiral magnets can be controlled experimentally via rotating the in-plane spins by means of magnetic, 42 electrical, 82 strain, 83 or temperature effects. 84 Moreover, the scalar-spin cases can be also realized via canting the spins along the out-of-plane direction by applying an external magnetic field, 85 a hydrostatic pressure, 86 or thermal fluctuations 87 in the presence of Dzyaloshinskii−Moriya interactions. 88 Thus, our findings are a crucial step to realize antiferromagnetic quantum spintronics integrating the properties of the QAHE and AFMs.…”