Putative helimagnetic phase in the kagome metal Co_3Sn_2-xIn_xS_2

Abstract

The exploration of topological electronic phases that result from strong\nelectronic correlations is a frontier in condensed matter physics. One class of\nsystems that is currently emerging as a platform for such studies are so-called\nkagome magnets based on transition metals. Using muon spin-rotation, we explore\nmagnetic correlations in the kagome magnet Co$_{3}$Sn$_{2-x}$In$_{x}$S$_{2}$ as\na function of In-doping, providing putative evidence for an intriguing\nincommensurate helimagnetic (HM) state. Our results show that, while the\nundoped sample exhibits an out-of-plane ferromagnetic (FM) ground state, at 5\n${\\%}$ of In-doping the system enters a state in which FM and in-plane\nantiferromagnetic (AFM) phases coexist. At higher doping, a HM state emerges\nand becomes dominant at the critical doping level of only $x_{\\rm cr,1}$\n${\\simeq}$ 0.3. This indicates a zero temperature first order quantum phase\ntransition from the FM, through a mixed state, to a helical phase at $x_{\\rm\ncr,1}$. In addition, at $x_{\\rm cr,2}$ ${\\simeq}$ 1, a zero temperature second\norder phase transition from helical to paramagnetic phase is observed,\nevidencing a HM quantum critical point (QCP) in the phase diagram of the\ntopological magnet Co$_{3}$Sn$_{2-x}$In$_{x}$S$_{2}$. The observed diversity of\ninteractions in the magnetic kagome lattice drives non-monotonous variations of\nthe topological Hall response of this system.\n