Magnetization of carbon-coated ferromagnetic nanoclusters determined by electron holography (original) (raw)
Related papers
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2000
In the present work, experiments aim at the encapsulation of foreign materials within hollow graphitic cage have been carried out for iron group metals (Fe, Co, Ni) using a modified arc-discharge (carbon arc) reactor. HRTEM (high resolution transmission electron miscroscope), and XRD (X-ray diffractometer) studies, for three carbon encapsulated materials, showing nanoparticles of both a metallic phase (a-Fe, g-Fe; hcp-Co, fcc-Co; fcc-Ni) and also a carbide phase (M 3 C, M =Fe, Co, Ni) are encapsulated in graphitic carbon. The magnetic measurement for the three as-made nanoparticles, indicating that the values of saturation magnetic moment of three nanoparticle are 37.6, 55.5 and 15.7% of the bulk ferromagnetic elements counterparts, respectively. The different comparison values (M r /M s ) of remanent magnetization (M r ) and saturation magnetization (M s ) suggest, the encapsulated Fe and Co nanoparticles are shown to be ferromagnetic with a ratio of remnant to saturation magnetization M r /M s 0.3; whereas, the encapsulated Ni nanoparticles exhibits superparamagnetic behavior at room temperature.
Microstructure and Magnetic Properties of Carbon-Coated Nanoparticles
In the present work, microstructure and superparamagnetic properties of two types of carbon-coated magnetic Ni and Fe nanoparticles [Ni(C) and Fe(C)] are reviewed. Highresolution transmission electron microscopy (HRTEM), electron diffraction (SAED), and x-ray diffraction (XRD) analyses have been used to reveal the distinct structural morphologies of Ni and Fe nanoparticles. Moreover, novel carbon-coated Ni nanoparticle assemblies offer us great opportunities for studying the mechanism of superparamagnetism in particle assemblies. Magnetization measurements [M(T) and M(H) curves] for assemblies of Ni nanoparticles indicate that modified superparamagnetic properties at T > T B , have been found in the assemblies of Ni(C) particles. The blocking temperature, T B , is determined to be near 115K under a certain applied field. Above T B , the magnetization M(H, T) can be described by the classical Langevin function L using the relation, M=M s (T ¼ 0) ¼ coth (mH=kT) À kT=mH. It is suggested that these assemblies of carbon-coated Ni nanoparticles have typical single-domain, field-dependent superparamagnetic relaxation properties. Finally, Mössbauer spectra and hyperfine magnetic fields at room temperature for the assemblies of Fe(C) nanoparticles confirm their distinct nanophases that were detected by structural analysis. Modified superparamagnetic relaxation is observed in the assemblies of Fe(C) nanoparticles, which is attributed to the nanocrystalline nature of the carbon-coated nanoparticles.
Applied Physics A, 2009
Using electron holography (interference electron microscopy) we have made measurements of the magnetic flux and magnetic field distribution around a carbon nanotube filled with iron. At the surface of the carbon nanotube, an iron particle with a radius of 30 nm and a length of 200 nm created a magnetic flux of 10 −15 Wb (Weber) and a magnetic field of 0.3-0.4 T (Tesla). The theory developed in this work is constrained to the case of cylindrical symmetry of the investigated ferromagnetic particles, but, in general, such studies can be made for ferromagnetic particles of any shape.
Magnetic properties of carbon-coated, ferromagnetic nanoparticles produced by a carbon-arc method
Journal of Applied Physics, 1994
The Kratschmer-Huffman carbon-arc method of preparing fullercnes has been used to generate carbon-coated transition metal (TM) and TM-carbide nanocrystallites. The magnetic nanocrystallites were extracted from the. soot with a magnetic gradient field technique. For TM=Co the majority of nanocrystals exist as nominally spherical particles, 0.5-S nm in radius. Hysteretic and temperature-dependent magnetic response, in randomly and magnetically aligned powder samples frozen in epoxy, correspond to fine particle magnetism associated with monodomain TM particles. The magnetization exhibits a unique functional dependence on H/T, and hysteresis below a blocking temperature T, . Below TR, the temperature dependence of the coercivity can be expressed as Hc=Hcu[ 1 -(T/TB)1'2], where HcO is the (1 K coercivity. 5882
Magnetic properties of carbon nanoparticles
IOP Conference Series: Materials Science and Engineering, 2012
Magnetization M (T, B) of powder and glassy samples containing carbon nanoparticles is investigated in the interval of temperatures T between ~ 3 300 K and magnetic fields B up to 5 T. Low-field magnetization, M (T), exhibits a strong magnetic irreversibility, which is suppressed above the field of ~ 1 T. The dependence of M (B) saturates at high temperatures above B ~ 2 T, magnetic hysteresis is observed already at 300 K. The values of the saturation magnetization, the coercivity field and the maximum blocking temperature are obtained. Analysis of the experimental data gives evidence for concentration of the magnetization close to the surface of the particles, which is consistent with the origin of magnetism in nanocarbon presumably due to intrinsic disorder and surface defects.
Two kinds of nickel nanoparticlesÐcarbon encapsulated Ni nanoparticles Ni(C) and pure Ni nanoparticles coated with NiO layers Ni(O) are successfully prepared. Structural characterizations (HR-TEM, SAED, and XRD) reveal their distinct morphological properties. Magnetization measurements for the assemblies of two kinds of Ni nanoparticles show a larger coercivity and remanence by a deviation between the zero-®eld-cooled and the ®eldcooled magnetization below the irreversibility temperature, T irr , for the assemblies of Ni(O) particles. This deviation may be explained as a typical nanocluster±glass behavior (collective behavior) due to ferromagnetic dipole±dipole interaction effects among the assemblies of Ni(O) particles. However, Ni(C) particles exhibit modi®ed superparamagnetic properties above the average blocking temperature of T B , which is determined to be around 115 K at 1000 Oe. Moreover, a gradual decrease in saturation magnetization is observed, which is attributed to the nanocrystalline nature of the encapsulated particles, coupled with possible carbon solution in Ni nanocrystals. #
Journal of Applied Physics
The crystal structure of Ca 3 Co 4 O 9 was investigated using high-resolution transmission electron microscopy (HRTEM) and the image-simulation method. The c * was 10.8Å and the b parameters were 4.56Å for the Ca 2 CoO 3 block and 2.82Å for the CoO 2 sheet. The [110] zone axis HRTEM images confirmed that Ca 3 Co 4 O 9 has a modulated layered structure with modulation. For the first time, the atomic positions of the Ca and Co atoms in the Ca 2 CoO 3 block were identified, corresponding to three rows of dark spots in the [110] direction. The observed HRTEM images for Ca 2 CoO 3 agreed well with the calculated images based on the structural model obtained by the Rietveld refinement method.