Room-temperature magnetic topological semimetal state in half-metallic Heusler Co$_2$TiX (X=Si, Ge, or Sn)

TL;DR

This paper predicts room-temperature magnetic topological semimetal states in ferromagnetic Co$_2$TiX Heusler compounds, revealing their potential for novel electronic properties and applications in spintronics.

Contribution

It identifies magnetic topological semimetal states in Co$_2$TiX compounds through first-principles calculations, demonstrating controllable Weyl nodes and high Curie temperatures.

Findings

Presence of three topological nodal lines without spin-orbit coupling

Formation of Weyl nodes with spin-orbit coupling depending on magnetization

Potential for room-temperature applications and anomalous Hall effects

Abstract

Topological semimetals (TSMs) including Weyl semimetals and nodal-line semimetals are expected to open the next frontier of condensed matter and materials science. Although the first inversion breaking Weyl semimetal was recently discovered in TaAs, its magnetic counterparts, i.e., the time-reversal breaking Weyl and nodal line semimetals, remain elusive. They are predicted to exhibit exotic properties distinct from the inversion breaking TSMs including TaAs. In this paper, we identify the magnetic topological semimetal state in the ferromagnetic half-metal compounds Co$_2$TiX (X=Si, Ge, or Sn) with Curie temperatures higher than 350 K. Our first-principles band structure calculations show that, in the absence of spin-orbit coupling, Co$_2$TiX features three topological nodal lines. The inclusion of spin-orbit coupling gives rise to Weyl nodes, whose momentum space locations can be controlled as a function of the magnetization direction. Our results not only open the door for the experimental realization of topological semimetal states in magnetic materials at room temperatures, but also suggest potential applications such as unusual anomalous Hall effects in engineered monolayers of the Co$_2$TiX compounds at high temperatures.