Researchers at Shenzhen University, the Japan Atomic Energy Agency, the National Institutes for Quantum Science and Technology (QST), the University of Tokyo, the University of Science and Technology of China, Xi'an Jiaotong University, Shenzhen Technology University (SZTU), and The Hong Kong Polytechnic University, have provided the first element-resolved confirmation of intrinsic carbon ferromagnetism at room temperature in a bulk, wafer-scale material. The result, obtained in a hyper-porous graphene network (HGN) grown across a 2-inch silicon wafer, adds carbon to the small list of room-temperature magnetic materials and offers a new, structurally tunable platform for exploring spintronic and magnetic applications of carbon allotropes.
Structural features of the hyper-porous graphene network (HGN). Structural characterization of the (HGN). (a) Optical image of HGN on a 2-inch Si wafer. (b) TEM image showing nanoscale pores. (c) Converted TEM sketch with pores (<2 nm) as hollow islands. (d-f), Plan-view HAADF TEM images: overview with pores (d), zoomed-in cross-linked edges (e), and atomic detail with 0.35 nm interlayer and 0.21 nm zigzag edge spacing (f). (g-i) Side-view TEM images: vertical layers (g), crosslinking features (h), and 0.12 nm armchair spacing (i). Image from: Advanced Materials
Claims of intrinsic magnetism in carbon have long been difficult to establish, since even a trace of ordinary magnetic contamination, iron, cobalt, or nickel, can produce a magnetic signal comparable to the faint ferromagnetism reported in some carbon systems, which typically sits near 10⁻³ emu/g or below in bulk graphite. Prior demonstrations of edge-localized magnetism in graphene nanoribbons and multi-spin nanographene molecules showed the underlying physics could work at the nanoscale, but establishing the same effect reliably in bulk carbon had remained an open problem, requiring evidence that carbon itself, not a contaminant, carries the magnetism, and a structural handle whose removal reversibly weakens the effect.
The team grew their porous graphene network using a plasma-assisted vapor process combined with low-energy electron irradiation, producing a three-dimensional mesh of curved, crosslinked graphene layers standing roughly perpendicular to the substrate, riddled with pores under 2 nm across and rich in exposed zigzag edges spaced more than roughly 1.4 nm apart. At room temperature, the material reached a saturation magnetization of 4.7 emu/g, more than three orders of magnitude above the graphite reference, equivalent to roughly one unpaired-electron-sized magnetic moment for every 17 carbon atoms.
To isolate carbon as the source, the team used X-ray magnetic circular dichroism (XMCD) tuned to the carbon absorption edge, obtaining a signal that reversed sign with the magnetic field or X-ray polarization as a genuine magnetic response should, while graphite and an amorphous-carbon control produced no comparable signal. XMCD scans at the characteristic absorption edges of iron, cobalt, and nickel detected none of their signatures, and inductively coupled plasma mass spectrometry (ICP-MS) showed that trace magnetic impurities could account for at most about 0.23% of the measured magnetization, in an intentionally generous estimate. Annealing the porous network into a denser carbon structure caused the carbon-specific magnetic signal to disappear, with magnetization falling back to roughly the amorphous-carbon control's level, tying the effect directly to the porous, edge-rich architecture rather than to the carbon composition alone.
Density functional theory calculations, combined with the XMCD estimate of about 0.03 μB per carbon atom (roughly half the 0.06 μB per atom derived from bulk magnetometry), showed that the spacing between opposing zigzag edges governs whether the material's local magnetic moments reinforce or cancel each other: edges separated by roughly 1.4 nm or more favor parallel spin alignment, while tighter spacing flips the preferred alignment. That structure-property link gives researchers a concrete design variable, pore geometry, to target if the magnetic state of carbon-based materials is to be made tunable, and the authors position the work as a platform for further exploring spintronic and magnetic device concepts built on carbon allotropes rather than conventional transition-metal magnets.