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The combination of highly sensitive Superconducting Quantum Interference Device (SQUID) with high quality nanoparticles allowed us to check for the first time simple classical models proposed nearly 50 years ago by Neel, Stoner and Wohlfarth. For nanoparticles containing about [10.sup.5] to [10.sup.6] [[Mu].sub.B] the quantitative agreement with the Neel-Brown theory of thermal activated magnetization reversal allowed us to identify unambiguously the magnetization reversal mechanism as uniform rotation. In the case of insulating barium ferrite nanoparticles containing about [10.sup.5] [[Mu].sub.B] and below 0.4 K, strong deviations from this model are found which are quantitatively in agreement with the predictions of the theory of macroscopic quantum tunneling of magnetization in the low dissipation regime. Index Terms - Single domain nanoparticles, magnetization reversal in unison, Neel - Brown theory, macroscopic quantum tunneling of magnetization.

An arc-discharge technique of filling carbon nanotubes with metals and their compounds helps determine the materials appropriate to yield distinct nanocomposite materials upon filling carbon nanotubes. The presence of an incomplete electronic shell in the most stable ionic state of the metal increases the susceptibility for the formation of continuous nanowires throughout the tubes. Interactions between growth of the nanotube and that of the filling contributes to the formation of a distinct helical filling morphology.

The influence of magnetic state (saturated or unsaturated states) on the ferromagnetic resonance damping in relaxing rare earth substituted [Y.sub.1-x]R[E.sub.x][Gd.sub.2][Fe.sub.5][O.sub.12] garnets (with RE = Dy Ho, Tb and x = 0;0.15;0.3;0.6) has been studied. The damping parameter [Alpha], as defined by Landau-Lifshitz equation, has been determined either by FMR at 10GHz ([[Alpha].sub.sat] for saturated state) or by measurement of the frequency dependence of the complex initial permeability in the 0.1GHz-10GHz band ([[Alpha].sub.unsat] for unsaturated state). in the saturated state the introduction of relaxing rare earth is found to increase significantly [[Alpha].sub.sat] values by more than one order of magnitude. On the contrary, although [[Alpha].sub.unsat] values also increase with rare earth concentration they stay in the same order of magnitude. It appears that [[Alpha].sub.unsat] is controlled either by the magnetic disorder introduced via the domain and domain wall structure or by the rare earth concentration. Index Terms - damping, gyromagnetism, garnets

The behavior of the magnetic properties of magnetite Fe3O4 irradiated by swift heavy ions is investigated by magnetization measurements. Although there is no induced structural phase transformation, both coercive field and saturation magnetization are sensitive to ion irradiation and exhibit different behaviors depending on the ion fluence range. In the low fluence regime, the coercive field increases, which is evidence for a strong pinning of magnetic domain boundaries by the induced defects. The magnetization shows a decrease in the saturation value and tends to reorient perpendicularly to the ion track axis. At high fluence, the initial magnetic properties of the sample are nearly restored. The changes in the magnitude and the direction of magnetization are interpreted by magnetostrictive effects related to the stress induced by irradiation. A phenomenological model is applied to reproduce the fluence evolution of the saturation magnetization, assuming relaxation of the stress induced around the core of defects of the tracks by overlapping effects at high fluence. The results are compared to those obtained in the case of yttrium iron garnet Y3Fe5O12. [ABSTRACT FROM AUTHOR]