Using magnetization measurements, we show that point defects in graphene - fluorine adatoms and irradiation defects (vacancies) - carry magnetic moments with spin 1/2. Both types of defects lead to notable paramagnetism but no magnetic ordering could be detected down to liquid helium temperatures. The induced paramagnetism dominates graphene's low-temperature magnetic properties despite the fact that maximum response we could achieve was limited to one moment per approximately 1000 carbon atoms. This limitation is explained by clustering of adatoms and, for the case of vacancies, by losing graphene's structural stability.Comment: 14 pages, 14 figure

Control of magnetism by applied voltage is desirable for spintronics applications. Finding a suitable material remains an elusive goal, with only a few candidates found so far. Graphene is one of them and attracts interest because of its weak spin-orbit interaction, the ability to control electronic properties by the electric field effect and the possibility to introduce paramagnetic centres such as vacancies and adatoms. Here we show that the magnetism of adatoms in graphene is itinerant and can be controlled by doping, so that magnetic moments are switched on and off. The much-discussed vacancy magnetism is found to have a dual origin, with two approximately equal contributions; one from itinerant magnetism and the other from dangling bonds. Our work suggests that graphene's spin transport can be controlled by the field effect, similar to its electronic and optical properties, and that spin diffusion can be significantly enhanced above a certain carrier density.

Superconducting layered transition metal dichalcogenides (TMDs) stand out among other superconductors due to the tunable nature of the superconducting transition, coexistence with other collective electronic excitations (charge density waves), and strong intrinsic spin-orbit coupling. Molybdenum disulfide (MoS2) is the most studied representative of this family of materials, especially since the recent demonstration of the possibility to tune its critical temperature, Tc, by electric-field doping. However, just one of its polymorphs, band-insulator 2H-MoS2, has so far been explored for its potential to host superconductivity. We have investigated the possibility to induce superconductivity in metallic polytypes, 1T- and 1T'-MoS2, by potassium (K) intercalation. We demonstrate that at doping levels significantly higher than that required to induce superconductivity in 2H-MoS2, both 1T and 1T' phases become superconducting with Tc = 2.8 and 4.6 K, respectively. Unusually, K intercalation in this case is responsible both for the structural and superconducting phase transitions. By adding new members to the family of superconducting TMDs, our findings open the way to further manipulate and enhance the electronic properties of these technologically important materials.

We report on an extensive investigation to figure out the origin of room-temperature ferromagnetism that is commonly observed by SQUID magnetometry in highly-oriented pyrolytic graphite (HOPG). Electron backscattering and X-ray microanalysis revealed the presence of micron-size magnetic clusters (predominantly Fe) emu/g, i.e., 5 orders of magnitude less than the saturation magnetization of Fe, and the whole subject remains controversial, especially concerning the role of possible contamination, as well as the mechanism responsible for the strong interaction required to lead to ferromagnetic ordering at room temperature.Trying to clarify the situation, we have carried out extensive studies of magnetic behaviour of HOPG crystals obtained from different manufacturers (ZYA-, ZYB-, and ZYH-grade from NT-MDT and SPI-2 and SPI-3 from SPI Supplies). These crystals are commonly used for studies of magnetism in graphite; e.g., ZYA-grade crystals were used in refs. [1,[3][4][5][6][7] and ZYH-grade in ref.[2]. We have also observed weak ferromagnetism, independent of temperature between 300K and 2K and similar in value to the one reported previously for pristine (non-irradiated) HOPG. Below, we show that the observed ferromagnetism in ZYA-, ZYB-, and ZYH-grade crystals is due to micron-sized magnetic inclusions (containing mostly Fe), which can easily be visualized by scanning electron microscopy (SEM) in the backscattering mode. Without the intentional use of this technique, the inclusions are easy to overlook. No such inclusions were found in SPI crystals and, accordingly, in our experiments these crystals were purely diamagnetic at all temperatures (no ferromagnetic signals at a level of 10 -5 emu/g).

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