Activated Layered Magnetism from Bulk TiN

TL;DR

This study reveals that increasing layer separation in TiN transforms it from a nonmagnetic bulk to a magnetic monolayer, highlighting a layer-dependent magnetic transition with potential for novel magnetic properties.

Contribution

The paper demonstrates a layer-dependent magnetic transition in TiN, showing that monolayer TiN becomes magnetic due to electron unpairing, which is a novel finding in layered transition metal nitrides.

Findings

Monolayer TiN is magnetic and likely a semiconductor.

Bilayer and trilayer TiN are nonmagnetic poor metals.

Antiferromagnetic states are energetically favored in monolayer TiN.

Abstract

The novel properties of a uniaxially-expanded TiN bulk arising from increasing the layer spacing from equilibrium are explored using a first-principles approach. We reveal a novel nonmagnetic-magnetic transition from a TiN bulk to its monolayer. We also investigate the electronic and magnetic structures of a few TiN atomic layers. We find that the bilayer and trilayer, like the TiN bulk, are nonmagnetic poor metals. On the other hand, the monolayer TiN is found to carry a magnetic moment on its Ti atoms, and likely be a semiconductor. The unpaired electron giving rise to magnetism on Ti is primarily in the orbital perpendicular to the layers, and we find it is freed to give rise to magnetism when the layers are slightly separated. We find two different antiferromagnetic states possible on the monolayer, as well as one ferromagnetic, with one of the antiferromagnetic being the lowest energy. The exchange couplings between Ti atoms in such a monolayer are calculated to be antiferromagnetic for both the nearest-neighbor and next-nearest-neighbor sites. We also analyze the binding nature of both the monolayer and bilayer TiN by searching for the predominant binding orbitals.