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Magnetic properties of Ni3C nanoparticles, about 40 nm in diameter, have been investigated. The sample exhibits weak ferromagnetic (FM), spin-glass (SG), and paramagnetic (PM) properties by alternating current susceptibility and direct current magnetization measurements. The freezing temperature of the SG phase at zero applied field is determined as TF0∼11.0 K. At T>TF0, a very weak ferromagnetism has been observed over a strong PM background. The Curie temperature TC is shown to exceed 300 K, and the ferromagnetism at 300 K is determined as about 0.02 emu/g∼6.7×10-4 μB per Ni3C formula unit. An anomalous dip appears in the temperature dependent coercivity HC(T) near the freezing temperature TF0. It reflects the distortedly reduced coercivity in the M(H) hysteresis loop measured at T∼TF0 with the applied sweeping field approaching H=0. This is attributable to the interaction between the SG and the weak FM phases. The possible origin of the magnetic moments that account for the observed FM, SG, and PM properties is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Co-based (Co and Co3O4) nanoparticles were self-integrated into SiO2 nanotubes with a methodology based on the use of a Co salt as a template structure for the formation of SiO2 nanotubes. Within the confinement of tubular matrix of SiO2, the nanofibres of cobalt precursor, i.e., [Co(NH3)6](HCO3)(CO3)·2H2O, were treated in a H2 atmosphere with different parameters. With a sufficient reduction on the cobalt precursor, sphere-like Co-based nanoparticles are obtained, being well aligned in the interior space of the SiO2 nanotubes. With an insufficient reduction, platelet-like Co-based nanoparticles are formed, being arranged in a random manner inside the SiO2 nanotubes. The sufficiently reduced Co–SiO2 nanocomposite exhibits an open hysteresis loop in the low field region (<3kOe) and a paramagnetic response in high field (>3kOe) at 300K. An observed wide separation between the zero-field-cooling (ZFC) and field-cooling (FC) curves over the whole temperature region has demonstrated a characteristic feature of ferromagnetism with a magnetically anisotropic barrier diverting the easy axis from the axis of the applied field. The predominant factor leading to this anisotropic potential barrier is attributed to the shape anisotropy native to the one-dimensional arrangement of Co-based nanoparticles within the tubular matrix, i.e. SiO2 nanotubes. [Copyright &y& Elsevier]

Abstract: A novel Co complex [Co(NH3)6Cl3] nanorods with diameters of 150–200nm and 2–2.5μm in length were synthesized successfully through a simple solution chemical route. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and superconducting quantum interference device (SQUID) system. We propose a possible reaction process for the formation of Co(NH3)6Cl3. A control experiment shows that PVP plays a soft-template to uniform the morphology and size of the products. [Copyright &y& Elsevier]