Ferromagnetism in C-doped SnO_2 thin films

摘要

Room temperature ferromagnetism (FM) was observed in laser ablated C-doped SnO_2 thin films grown on LaAlO_3 substrates. The greatest value of the saturated magnetization (at 1 T) is found in SnO_2 films doped with 1% of C (about 16 emu/cm~3) and reduces lightly as the C concentration increases. By subtracting the base of pure SnO_2 that is also magnetic, one can find that C-doping actually enhances ferromagnetism in the host SnO_2. It suggests that carbon really causes defect-induced magnetism of about 3.91 μb/C into SnO_2. Measurements on C-doped SnO_2 bulks show that the observed properties are unique for films (lower dimensions, having surface/interface effect). The investigation on thickness dependence shows a change in magnetization when going from thin to thick films, implying that somehow if magnetism is due to defects then those must be located more on or near the surface than in deeper layers. Anisotropy is also observed, enforcing the assumption for the origin of magnetism due to defects in C-doped SnO_2.