Kagome lattice promotes chiral spin fluctuations

Magnetic materials with tilted electron spins often exhibit conducting behaviour that cannot be explained from semiclassical theories without invoking fictitious (emergent) electromagnetic fields. Quantum-mechanical models explaining such phenomena are rooted in the concept of a moving quasiparticle’s Berry phase[1, 2], driven by a chiral (left- or right-handed) spin-habit. Dynamical and nearly random spin fluctuations, with a slight bent towards left- or right-handed chirality, represent a promising route to realizing Berry-phase phenomena at elevated temperatures[3–6], but little is known about the effect of crystal lattice geometry on the resulting macroscopic observ-ables. Here, we report thermoelectric and electric transport experiments on two metals with large magnetic moments on a triangular and on a slightly distorted kagom´e lattice, respectively. We show that the impact of chiral spin fluctuations is strongly enhanced for the kagom´e lattice. Both these spiral magnets have similar magnetic phase diagrams including a periodic array of magnetic skyrmions. However, our modelling shows that the geometry of the kagom´e lattice, with corner-sharing spin-trimers, helps to avoid cancellation of Berry-phase contributions; spin fluctuations are endowed with a net chiral habit already in the thermally disordered (paramagnetic) state. Hence, our observations for the kagom´e material contrast with theoretical models treating magnetization as a continuous field[7–11], and emphasize the role of lattice geometry on emergent electrodynamic phenomena.