Electrochemical thinning of Co kagome-lattice layers in ferromagnetic Co3Sn2S2 thin films by bias-induced Co dissolution

Abstract

Solid–liquid interfaces made of functional inorganic materials and liquid electrolytes exhibit various interesting responses by applying an electric bias across the interface. Using an electric-double-layer device fabricated on a thin-film channel of magnetic Weyl semimetal Co3Sn2S2 with an ionic liquid gate electrolyte, we show that the conducting channel thickness can be effectively decreased by applying a negative gate voltage. The application of a gate voltage of −6 V at 250 K gives rise to an irreversible increase in the channel resistance. Transmission electron microscopy reveals that the thickness of the crystallized Co3Sn2S2 region is decreased by applying the negative bias, leaving a Co-poor disordered region on top of the Co3Sn2S2 layer. These results suggest that the preferential dissolution of Co is driven under the application of the negative bias, which leads to the disconnection of Co kagome-lattice layer that is mainly responsible for electrical conduction in Co3Sn2S2. Distinct from conventional bottom-up film growth approaches, this top-down thickness control enables us to examine the thickness dependence of the anomalous transport properties of Co3Sn2S2 in a single sample. The present finding will be useful for experimentally verifying the theoretically discussed ultrathin-film properties of the magnetic Weyl semimetal Co3Sn2S2.