Morphology and ferromagnetism of Ge nanostructure

Abstract

A series of Ge films with varying thickness is prepared by plasma enhanced chemical vapor deposition technology. With the thickness of the sample becoming thinner, the sample shows ferromagnetism. When the 12-nm-thick sample is annealed at 300℃, the partile size becomes smaller, and thus the number of interface defects between the particles increases, so the sample gives a largest magnetic signal at room temperature (50 emu/cm3). FC-ZFC measurement shows that Curie temperature is 350 K. For a higher temperature (600 ℃, the coalescence of small Ge particles makes surface area decline, so magnetic signal becomes weak. With the thickness being 6 nm, the paramagnetism and the ferromagnetism coexist in the 6-nm-thick Ge film. When the 6-nm-thick sample is annealed under nitrogen atmosphere at 300 ℃, the sample only shows ferromagnetism. However, annealed at 600 ℃, the sample only presents paramagnetism. With the annealing temperature changing, the 12-nm-thick film and the 6-nm-thick film show different magnetic phenomena. Particle size and particle distribution cause different magnetic phenomena. It is supposed that the Ge nannostructure unpaired electrons are provided mainly by the interface defect between Si matyix and Ge film and the surface defect of Ge particles. The ferromagnetism coupling of the unpaired electrons is related to the distribution of sample particles and the junction among particles. The fusion between particles will reduce the ferromagnetism of the sample.