We report on the experimental observation of magnetic hysteresis up to room temperature in thiol-capped Au nanoparticles with 1.4 nm size. The coercive field ranges from 860 Oe at 5 K to 250 Oe at 300 K. It is estimated that the Au atoms exhibit a magnetic moment of $\mu =0.036{\mu }_B$. However, Au nanoparticles with similar size but stabilized by means of a surfactant, i.e., weak interaction between protective molecules and Au surface atoms, are diamagnetic, as bulk Au samples are. The apparent ferromagnetism is consequently associated with $5d$ localized holes generated through Au-S bonds. These holes give rise to localized magnetic moments that are frozen in due to the combination of the high spin-orbit coupling (1.5 eV) of gold and the symmetry reduction associated with two types of bonding: Au-Au and Au-S.

The onset of ferromagnetism has been experimentally observed in small Pd particles of average diameter 2.4 nm. High-resolution studies reveal that a high percentage of the fcc particle exhibits single and multiple twinning boundaries. The spontaneous magnetization close to $0.02\mathrm{e}\mathrm{m}\mathrm{u}/\mathrm{g}$ seems to indicate that only a small fraction of atoms holds a permanent magnetic moment and contributes to ferromagnetism. The possible origin of ferromagnetism is briefly discussed according to different models recently reported.

Since the prediction of Liu and Cohen [Science 245, 841 (1989)] of the potential extraordinary mechanical properties of crystalline $\mathrm{\beta -}{\mathrm{C}}_{\mathrm{3}}{\mathrm{N}}_{\mathrm{4}},$ many authors have attempted its synthesis. However, in most cases, the obtained materials are amorphous phases with a complex bonding structure. Their characterization is complicated due to the absence of a reference compound, the lack of long-range order, and the poor knowledge about their bonding structure. In this article, we present ${}^{\mathrm{1}}\mathrm{H},$ ${}^{\mathrm{13}}\mathrm{C},$ and ${}^{\mathrm{15}}\mathrm{N}$ solid-state nuclear magnetic resonance (NMR) measurements for the determination of the bonding types in amorphous ${\mathrm{CN}}_x$ films. NMR measurements do not require long-range order and are able to clearly identify the signals from the ${\mathrm{sp}}^2$ - and ${\mathrm{sp}}^3$ -bonded phases. The analysis of the data obtained by other characterization techniques, such as infrared spectroscopy, x-ray photoelectron spectroscopy, electron energy-loss spectroscopy, and x-ray absorption near-edge spectroscopy on the same sample, based on the information acquired by NMR, enables the description of a structure model for the studied amorphous-${\mathrm{CN}}_x$ phase prepared by dc-magnetron sputtering and to revise the interpretation found in the literature.