Quantum-Confined Tunable Ferromagnetism on the Surface of a van der Waals Antiferromagnet NaCrTe2

TL;DR

This study reveals that NaCrTe2 exhibits quantum-confined ferromagnetism on its surface, which can be tuned via surface doping, providing a new platform for exploring low-dimensional magnetic states.

Contribution

It demonstrates the existence of tunable 2D ferromagnetism on the surface of a van der Waals antiferromagnet, supported by experimental and theoretical evidence.

Findings

Surface ferromagnetism persists above bulk Ne9el temperature.

Exchange splitting can be controlled by alkali-metal doping.

Surface state resembles ferromagnetic monolayer CrTe2.

Abstract

The surface of three-dimensional materials provides an ideal and versatile platform to explore quantum-confined physics. Here, we systematically investigate the electronic structure of Na-intercalated CrTe2, a van der Waals antiferromagnet, using angle-resolved photoemission spectroscopy and ab-initio calculations. The measured band structure deviates from the calculation of bulk NaCrTe2 but agrees with that of ferromagnetic monolayer CrTe2. Consistently, we observe an unexpected exchange splitting of the band dispersions, persisting well above the N\'eel temperature of bulk NaCrTe2. We argue that NaCrTe2 features a quantum-confined 2D ferromagnetic state in the topmost surface layer due to strong ferromagnetic correlation in the CrTe2 layer. Moreover, the exchange splitting and the critical temperature can be controlled by surface doping of alkali-metal atoms, suggesting a feasible tunability of the surface ferromagnetism. Our work not only presents a simple platform to explore tunable 2D ferromagnetism but also provides important insights into the quantum-confined low-dimensional magnetic states.