Magnetic properties of carbon-coated rare-earth carbide nanocrystallites produced by a carbon arc method

Abstract

Carbon-coated gadolinum and holmium carbide nanocrystallites have been generated using a modification of the Huffman-Krätschmer carbon arc process. Bulk amounts of these particles were isolated from the other by-products using a magnetic field gradient. Transmission electron microscopy revealed the presence of 10–50 nm diameter crystallites coated with numerous graphitic layers. The nanocrystallite phases were identified as Gd2C3 and Ho2C3, respectively, by x-ray and electron diffraction. Magnetization measurements were performed using a superconducting quantum interference device magnetometer between ±5 T at temperatures ranging from 4 to 200 K. The magnetization curves were shown to scale as a function of H/T. The RE3+ sites in RE2C3 have C3 site symmetry. For Gd2C3 the universal curve was fit with a Brillouin function consistent with the Gd3+ free-ion ground-state values of J=7/2 and g=2. The 5I8 Ho3+ free-ion ground state is split, presumably due to a C3 symmetry crystal field. Consequently, for Ho2C3 the Ho3+ free-ion parameters could not be used to fit the experimental data. Empirical fits to the Brillouin function yield a reduced moment of 7.5μB, compared to the free-ion value of 10.6μB. A similarly reduced moment was observed in holmium-containing endohedral fullerenes.

Mechanics of carbon nanotubes

“…Early attempts to make filled CNTs using arc evaporation have also resulted in filled carbon nano-particles rather than filled CNTs. The foreign fillers include most metallic elements [265][266][267][268][269][270][271][272][273][274][275][276], magnetic materials [277][278][279][280][281] and radioactive materials [282,283], and are surrounded by a carbon shell. One of the most well-known commercial applications of such filled nano-particles is the invention of the so-called Technegas [284,285] , which is essentially radioactive material coated with carbon and used as an imaging agent in the detection of lung cancer.…”

Magnetic Properties of Graphitically Encapsulated Nickel Nanocrystals

“…This tends to limit potential industrial applications and even scientific evaluation of nanocrystalline properties. A recent breakthrough in this regard is encapsulation of nanocrystals with chemically stable species such as graphitic layers, [16][17][18][19][20][21][22][23][24][25][26][27][28][29] which not only protects the nanocrystals from environmental degradation, but is also believed to be benign insofar as the intrinsic nanocrystalline magnetic properties are concerned.…”

“…The recent studies of the graphitic encapsulation of metal carbides [16][17][18][19][20][21][22][23] have promoted an extensive research on similar protection of ferromagnetic materials, e.g., Fe, Co, and Ni. [24][25][26][27][28][29] Appropriately encapsulated ferromagnetic materials may find applications ranging from ferrofluids and recording media to novel biomedical applications such as drug delivery and immunoassays.…”

Interface Structure of Niobium Carbide-Encapsulating Carbon Nanocapsules Studied by High-Resolution Transmission Electron Microscopy

“…[3][4][5][6][7][8][9][10][11][12][13] Various pure metals and metal carbides have been encapsulated in these nanospaces. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] In particular, it has been reported that composites of niobium carbide (NbC)-encapsulating CNCs and C matrices show a superconducting critical temperature of 10.7 K and form three-dimensional superconducting single-electron tunneling networks. 33 This tunneling effect originates from the graphene/NbC interfaces in the composites.…”