J. Mater. Sci. Technol., 2010, 26(11), 1051-1056. Structure and Magnetic Properties of Boron-oxide and Boron-nitride Coated Iron Nanocapsules W.S. Zhang 1,2)† , J.G. Zheng 3) , E. Br¨ uck 4) , P.Z. Si 1) , D.Y. Geng 1) and Z.D. Zhang 1) 1) Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, China and International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016, China 2) College of Physics & Electronic Engineering, Taizhou University, Taizhou 317000, China 3) Electron Probe Instrumentation Center (EPIC), Northwestern University, 2225N Campus Drive, 1156 MLSF, Evanston IL 60208-3108, USA 4) Van der Waals-Zeeman Instituut, Universiteit van Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam, The Nether- lands [Manuscript received September 10, 2009, in revised form July 12, 2010] The boron-oxide coated iron nanocapsules have been prepared by arc-discharge in a mixture of diborane and nitrogen, and then the boron-nitride coated iron nanocapsules by a subsequent annealing under a nitrogen atmosphere at 1100 ◦ C. After the arc-discharge, the boron-oxide coated iron nanocapsules form, which show an amorphous surface layer of B 2 O 3 (and/or B) and a core of γ -Fe, α-Fe, FeB phases. After being annealed, part of the α-Fe phase transforms to the γ -Fe phase, and the FeB phase decomposes while the BN phase forms. The BN shell structure formed in the BN encapsulating iron nanocapsules is incomplete. Magnetic properties of the boron-oxide coated and the boron-nitride coated iron nanocapsules were compared and discussed in terms of the particles ′ sizes, the phase components, and the surface structures. KEY WORDS: Arc discharge; Nanocapsules; Magnetic properties 1. Introduction Magnetic nanoparticles can be widely used in magnetic storage media, magnetic toner in xerogra- phy, catalysis, ferrofluids, clinical drug delivery, etc. Nanocapsules are the nanoparticles with shell/core structure [1,2] . The nanocapsules have attracted great interest, because of the protective coating of nanopar- ticles, which are usually pyrophoric and easily ox- idized. It is a common fact that the protective coating of nanoparticles has a paramount impor- tance for their application in the ambient environ- ment. The nanocapsules with different shells, such as graphite [3–5] , tungsten disulphide [6,7] , boron oxide [8] , silica oxide [9] , polymer [10] and boron nitride [11,12] , have been synthesized. The structure and magnetic properties of † Corresponding author. Ph. D.; E-mail address: wszhangimr@hotmail.com; wszhang@tzc.edu.cn (W.S. Zhang). nanoscaled materials are different from those of the bulk materials. The studies on magnetic nanopar- ticles are helpful for understanding the behavior of electrons and spins in low dimensions. It has been a direct probe on the superparamagnetic phenom- enon in Co nanoparticles [13] . For nanoparticles, even a small deviation in the particle size can lead to a large change in the blocking temperature. Fundamen- tal magnetic parameters, such as the barrier height of the anisotropy energy, the distribution of the energy barrier and the flipping times, can be estimated from zero-field-cooled (ZFC) and field-cooled (FC) temper- ature dependence of magnetization of the magnetic nanoparticles [8,14–17] . In the present work, we try to prepare the boron-oxide encapsulating iron nanoparticles, by arc- discharge in a mixture of diborane and nitrogen, then the boron-nitride coated iron nanocapsules by a sub- sequent annealing under a nitrogen atmosphere at 1100 ◦ C. The structures of the as-prepared and as-