Room temperature ferromagnetic-like behavior in fullerene photopolymerized films treated with monatomic hydrogen is reported. The hydrogen treatment controllably varies the paramagnetic spin concentration and laser induced polymerization transforms the paramagnetic phase to a ferromagnetic-like one. Excess laser irradiation destroys magnetic ordering, presumably due to structural changes, which was continuously monitored by Raman spectroscopy. We suggest an interpretation of the data based on first-principles density-functional spin-unrestricted calculations which show that the excess spin from mono-atomic hydrogen is delocalized within the host fullerene and the laser-induced polymerization promotes spin exchange interaction and spin alignment in the polymerized phase.

Synthetic nitrogen-doped diamond single crystals have various high-tech applications, but their electronic properties have not been sufficiently studied. In this research, we investigated temperature dependencies in the range T = (550–1143) K of the electrical resistivity and Hall mobility in synthetic single-crystal Ib-type diamonds doped with nitrogen during growth. A series of experimental samples were cut from diamond crystals grown by temperature gradient high-pressure high-temperature (TG-HPHT) and chemical vapor deposition (CVD) methods. They contain (0.085–6.5) × 1019 cm−3 single substitutional nitrogen atoms (C-centers) as measured by optical spectrometry methods. The Hall mobility of free electrons decreases from 600 to 150 cm2 V−1 s−1 in the CVD grown sample with the lowest N content and from 300 to 100 cm2 V−1 s−1 in highly doped HPHT grown samples in the temperature range of 550–900 K. At T = (900–1100) K, the mobility decreases to 50 cm2 V−1 s−1 in highly doped samples. The activation energies of electrical conductivity Ea and impurity-to-band energies of nitrogen donors ED decrease with increasing N concentration in the ranges (1.55–1.32) and (1.63–1.33) eV, respectively. The lowest compensation ratio k ∼ 1% in the moderately doped CVD diamond is unique for n-type diamonds. Typical values of k in highly N-doped crystals are in the range of 10%–20%, facilitating the use of N-doped diamonds in durable high-temperature electronic devices.

In this work, we demonstrate that cutting diamond crystals with a laser (532 nm wavelength, 0.5 mJ energy, 200 ns pulse duration at 15 kHz) produced a ≲20 nm thick surface layer with magnetic order at room temperature. We measured the magnetic moment of five natural and six CVD diamond crystals of different sizes, nitrogen contents and surface orientations with a SQUID magnetometer. A robust ferromagnetic response at 300 K was observed only for crystals that were cut with the laser along the (100) surface orientation. The magnetic signals were much weaker for the (110) and negligible for the (111) orientations. We attribute the magnetic order to the disordered graphite layer produced by the laser at the diamond surface. The ferromagnetic signal vanished after chemical etching or after moderate temperature annealing. The obtained results indicate that laser treatment of diamond may pave the way to create ferromagnetic spots at its surface.