First-principles and experimental investigation of d0 magnetism in proton-implanted HOPG

Abstract

In this study, we report a combined experimental and first-principles investigation of the emergence of room temperature ferromagnetism in Highly Oriented Pyrolytic Graphite (HOPG) irradiated with 1.2 MeV proton (H+) ion at fluences ranging from 10–85 pC μm−2. Vibrating Sample Magnetometry reveals the enhancement of ferromagnetic signal at the ion fluence of 35 pC μm−2 with saturation magnetization 0.89 emu g−1. X-ray diffraction and Raman spectroscopy reveal that the ion irradiation in implantation regime induced lattice disorder, reduced crystallite size and origin of D-band at 1347.84 cm−1, indicating disorder in the sp2 network at the ion fluence of 35 pC μm−2. SRIM simulations reveal the formation of maximum carbon vacancy near the proton stopping range and the decline in the inter-vacancy distance with increasing fluence. First-principles calculations, utilizing spin-polarized DFT, indicates that a single monovacancy (VC1) creates no net magnetic ordering in HOPG system, while hydrogen-passivated vacancies (HC1) produce a significant local magnetic moment (2.9 μB). Divacancies (VC1-C2 & VC1-C3) stabilize ferromagnetism through exchange coupling with magnetic moment of 2.10 μB to 2.13 μB. Hydrogen at interstitial sites (Hint) further induces less spin-polarization but contributed to interlayer expansion, which has been corroborated with the XRD/Raman analysis of 35 pC μm−2 irradiated sample. This combined experimental and theoretical study provides microscopic understanding of defect induced d0-magnetism in HOPG and suggests pathway for achieving lightweight magnetic materials for spintronic applications. © 2026 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved. This article is available under the terms of the https://publishingsupport.iopscience.iop.org/iop-standard/v1.