We provide evidence that proton irradiation of energy 2.25 MeV on highly oriented pyrolytic graphite samples triggers ferro- or ferrimagnetism. Measurements performed with a superconducting quantum interferometer device and magnetic force microscopy reveal that the magnetic ordering is stable at room temperature.

We have studied the magnetization of various well characterized samples of highly oriented pyrolitic graphite (HOPG), Kish graphite, and natural graphite to investigate the recently reported ferromagneticlike signal and its possible relation to ferromagnetic impurities. The magnetization results obtained for HOPG samples for applied fields parallel to the graphene layers—to minimize the diamagnetic background—show no correlation with the magnetic impurity concentration. Our overall results suggest an intrinsic origin for the ferromagnetism found in graphite. We discuss possible origins of the ferromagnetic signal.

ZnO films were prepared by pulsed laser deposition on $a$ -plane sapphire substrates under ${\mathrm{N}}_2$ atmosphere. Ferromagnetic loops were obtained with the superconducting quantum interference device at room temperature, which indicate a Curie temperature much above room temperature. No clear ferromagnetism was observed in intentionally Cu-doped ZnO films. This excludes that Cu doping into ZnO plays a key role in tuning the ferromagnetism in ZnO. 8.8% negative magnetoresistance probed at $5\mathrm{K}$ at $60\mathrm{kOe}$ on ferromagnetic ZnO proves the lack of $s\text{-}d$ exchange interaction. Anomalous Hall effect (AHE) was observed in ferromagnetic ZnO as well as in nonferromagnetic Cu-doped ZnO films, indicating that AHE does not uniquely prove ferromagnetism. The observed ferromagnetism in ZnO is attributed to intrinsic defects.

Elemental carbon represents a fundamental building block of matter and the possibility of ferromagnetic order in carbon has attracted widespread attention. However, the origin of magnetic order in such a light element is only poorly understood and has puzzled researchers. We present a spectromicroscopy study at room temperature of proton irradiated metal-free carbon using the elemental and chemical specificity of x-ray magnetic circular dichroism. We demonstrate that the magnetic order in the investigated system originates only from the carbon $\pi$-electron system.

We have investigated the magnetic properties of pure ZnO thin films grown under ${\text{N}}_2$ pressure on $a$-, $c$-, and $r$-plane ${\text{Al}}_2{\text{O}}_3$ substrates by pulsed-laser deposition. The substrate temperature and the ${\text{N}}_2$ pressure were varied from room temperature to $570°\text{C}$ and from 0.007 to 1.0 mbar, respectively. The magnetic properties of bare substrates and ZnO films were investigated by SQUID magnetometry. ZnO films grown on $c$- and $a$-plane ${\text{Al}}_2{\text{O}}_3$ substrates did not show significant ferromagnetism. However, ZnO films grown on $r$-plane ${\text{Al}}_2{\text{O}}_3$ showed reproducible ferromagnetism at 300 K when grown at $300–400°\text{C}$ and 0.1–1.0 mbar ${\text{N}}_2$ pressure. Positron annihilation spectroscopy measurements as well as density-functional theory calculations suggest that the ferromagnetism in ZnO films is related to Zn vacancies.