Ferromagnetism in β-Ag2Se topological semimetal

Abstract

High-temperature ferromagnetism in materials composed of non-magnetic constituents is one of the most intriguing aspects in condensed matter physics as well as materials science. Beyond oxide compounds where the ferromagnetism is mainly induced by dilute magnetic dopants, a variety of unusual ferromag- netic materials, mostly fabricated artificially to control the magnetic and electronic properties, have been investigated for spintronic device applications. The unexpected ferromagnetism, attributed to strain and structural defects or proximity and interfacial effects, is now extended to quantum materials, despite prevailing controversy on its physical origin. Recently, the ferromagnetism observed in topological mate- rials with high mobility arising from the linear energy dispersion invokes new interest in the field of spintronics. Here, we report experimental verification of peculiar high-temperature ferromagnetism in β- Ag2Se topological semimetal, composed of non-magnetic constituents. We have fabricated stoichiometric Ag2Se (S-Ag2Se) and Ag-vacant Ag2Se (V-Ag2Se) samples. Contrary to non-magnetic behavior of S-Ag2Se, V- Ag2Se shows distinct ferromagnetic response up to room temperatures. First-principles calculations de- monstrate that the ferromagnetic ordering occurs only in V-Ag2Se if there is finite Hubbard U, which can be explained by self-trapped magnetic polaron model with strong p-d hybridization. High-temperature fer- romagnetism, especially in topological materials, allows exploring a significant new direction in material engineering for spintronic applications.