Room-temperature ferromagnetism in undoped GaN and CdS semiconductor nanoparticles

Room-temperature ferromagnetism has been observed in undoped GaN and CdS semiconductor nanoparticles of different sizes with the average diameter in the range 10–25 nm. These nanoparticles were synthesized by simple routes and thoroughly characterized by various techniques. Magnetization measurements at room temperature show that these nanoparticles are ferromagnetic with a saturation magnetization of ∼10⁻³ emu∕gm, which is comparable to that observed in nanoparticles of nonmagnetic oxides. On the other hand, agglomerated particles of GaN and CdS exhibit diamagnetism or ferromagnetism with small saturation moments. Furthermore, the saturation magnetic moment decreases with the increase in particles size, suggesting that ferromagnetism is due to the defects confined to the surface of the nanoparticles, while the core of the particles remains diamagnetic. The observation of ferromagnetism is consistent with the prediction that Ga vacancies in GaN give rise to a ferromagnetic ground state.