Enhanced room temperature ferromagnetism in nanostructured MoS2 flakes by hydrogen post-treatment: Combined experimental and first-principles-based studies

TL;DR

This study combines experimental and first-principles approaches to enhance room-temperature ferromagnetism in nanostructured MoS2 flakes through hydrogen treatment, revealing defect and edge modifications as key factors.

Contribution

It provides new insights into how hydrogen irradiation and annealing induce ferromagnetism in MoS2 by modifying defects and edges, supported by both experiments and DFT calculations.

Findings

Hydrogen treatment increases ferromagnetism in MoS2.

Maximum saturation magnetization achieved is 2.7 emu/g at 200°C.

DFT shows edge and defect modifications significantly enhance magnetization.

Abstract

We meticulously study the individual effects of hydrogen irradiation and annealing on the electronic structure and magnetic properties of nanostructured MoS2 thin films grown through Chemical Vapor Deposition (CVD). The role of edge-terminated structure and point defects to induce room-temperature ferromagnetism (RTFM) is thoroughly investigated. The nanostructured pristine MoS2 thin films show the formation of a pure 2-H MoS2 phase, confirmed by X-ray diffraction (XRD) and Raman spectroscopy. Pristine MoS2 thin films are independently annealed in a reducing hydrogen environment and irradiated with low-energy hydrogen ions to study the significance of point defects like sulfur vacancies. RTFM with saturation magnetization value (Ms: 1.66 emu/g) has been observed in the pristine film. Magnetization increases after irradiation and annealing processes. However, hydrogen annealing at a temperature of 200oC exhibits a maximum Ms value of 2.7 emu/g at room temperature. The increase in ferromagnetism is attributed to an increment in sulfur vacancies, hydrogen adsorption with sulfur, and modification in edges, which is confirmed by the analysis of Electron probe micro-analyzer (EPMA), X-ray photoelectron spectroscopy (XPS), and Field emission scanning electron microscopy (FESEM) measurements. The Density Functional Theory (DFT) calculations have demonstrated that the edge-oriented structure of MoS2 exhibits a magnetization value of 3.2 {\mu}B. Additionally, introducing an S-vacancy and H-adsorption in a parallel position to the sulfur further enhances the magnetization value to 3.85 {\mu}B and 3.43 {\mu}B respectively. These findings align broadly with our experimental results.