Structure and magnetic properties of boron-oxide-coated Fe(B) nanocapsules prepared by arc discharge in diborane

Abstract

The structure and magnetic properties of boron-oxide-encapsulated magnetic nanocapsules fabricated by arc discharge in diborane $({\mathrm{B}}_{2}{\mathrm{H}}_{6})$ atmosphere have been investigated. The structure of boron-oxide-coated Fe(B) nanocapsules is different from that of carbon-coated nanocapsules. In contrast to carbon-coated nanocapsules consisting of a crystalline shell of graphite and a core of \ensuremath{\alpha}-Fe and/or ${\mathrm{Fe}}_{3}\mathrm{C},$ boron-oxide-coated Fe nanocapsules show an amorphous surface layer and a core of \ensuremath{\alpha}-Fe [and \ensuremath{\alpha}-Fe(B) solid solution], \ensuremath{\gamma}-Fe, FeB, and/or ${\mathrm{Fe}}_{3}\mathrm{B}$ phases. The loop shift in the hysteresis loop indicates the existence of the exchange bias between ferromagnetic and antiferromagnetic components at room temperature. The ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ phase contributes to the exchange bias as antiferromagnetic components. A very wide energy barrier distribution exists in the Fe(B) nanocapsules.