Synthesis, characterization, and magnetic properties of carbon- and boron-oxide-encapsulated iron nanocapsules.

Carbon- and boron-oxide-encapsulated iron nanocapsules have been synthesized by arc discharge in methane (CH4) and diborane (B2H6) atmospheres respectively. The characterization and magnetic properties of carbon- and boron-oxide-encapsulated iron nanocapsules [abbreviated as Fe(C) and Fe(B) respectively] were investigated and compared. The structure of the Fe(B) nanocapsules is different from that of the Fe(C) nanocapsules. The Fe(C) nanocapsules consist of a crystalline graphite shell and a core of alpha-Fe and/or Fe3C. The Fe(B) nanocapsules consist of an amorphous boron-oxide layer and a core of Fe(B) solid solution, alpha-Fe, gamma-Fe, FeB, and/or Fe3B phases. The saturation magnetizations of both the Fe(C) and the Fe(B) nanocapsules below 300 K decrease monotonically with increasing temperature. The coercivities of the Fe(C) and Fe(B) nanocapsules are almost 2 orders of magnitude higher than that of bulk Fe. The temperature dependence of magnetization at high temperatures indicates the existence of some phase transformations.