Chengfu Pan

Ferromagnetism in hydrogenated N-doped amorphous carbon films

Room temperature ferromagnetism has been observed in hydrogenated N-doped amorphous carbon films (a-CNx:H) prepared by plasma enhanced chemical vapor deposition. The magnetization of the films changed depending on the ratio (R) of the flow rate of nitrogen to that of methane during deposition and on the annealing temperature. The highest magnetization of the as-deposited samples was obtained with R = 4. Annealing the films at 300 °C resulted in a significant increase in the magnetic moment compared to that of the as-deposited films. When the annealing temperature was above 500 °C, the magnetic moment of the samples decreased. No ferromagnetic impurities could be detected. The ferromagnetism of the a-CNx:H film is attributed mainly to spin-polarization of the p orbitals of the N adatoms on the surface or in the interlayers of irregular carbon.

Ferromagnetism in Ge/SiO2 multilayer films

The onset of room-temperature (RT) ferromagnetism (FM) has been experimentally observed in amorphous Ge/SiO2 multilayer films. Both the thickness of the individual layers of SiO2 and that of the Ge layers can influence the ferromagnetic order of the samples. The saturation magnetization (MS) reached a maximum of 18.3 emu/cm3 at RT for the film with structure [Ge(5 nm)/SiO2(8 nm)]3. The zero-field-cooled and field-cooled curves for the film show the coexistence of ferromagnetic and diamagnetic components. Obvious magnetic domains were observed in all of the samples. Ge forms mainly Ge–Ge bonds. In addition, Photoluminescence from interband indirect recombination and transitions between discrete energy levels in Ge nanostructures were observed. The FM in the Ge/SiO2 multilayer films can be attributed to both the quantum size effect and coupling of unpaired spins among the Ge nanostructures. The coupling tends to make the unpaired spins align in a ferromagnetic manner.