Microwave permeability spectra of single Co nanotube under equilibrium state have been studied by micromagnetics simulation.More than four obvious resonance peaks have been found(11.72,24.20,33.18 and 39.55 GHz).Such large resonance frequency cannot be found in other traditional magnetic materials.The configurations of magnetic moments along the nanotube have been simulated.The results show that the top end of nanotube has a"flow-out"pattern of magnetic moments configuration.The bottom end has a"flow-in"pattern of magnetic moments configuration.The magnetic moments within the main body of nanotube are aligned perfectly along the length of nanotube.The magnitude of natural resonance peak is strongly related to the volume fraction of a zone,which has the same orientation of magnetic moments.Large microwave permeability values have been found for single nanotube.The generalized Snoek’s law has been used to validate the micromagnetics simulations in this paper.
The Fe-Cu-Nb-Si-B alloy nanocomposite containing two ferromagnetic phases （amorphous phase and nanophase phase） is obtained by properly annealing the as-prepared alloys. High resolution transmission electron microscopy （HR- TEM） images show the coexistence of these two phases. It is found that Fe-Si nanograins are surrounded by the retained amorphous ferromagnetic phase. Mossbauer spectroscopy measurements show that the nanophase is the D03-type Fe- Si phase, which is employed to find the atomic fractions of resonant 57Fe atoms in these two phases. The microwave permittivity and permeability spectra of Fe-Cu-Nb-Si-B nanocomposite are measured in the frequency range of 0.5 GHz- 10 GHz. Large relative microwave permeability values are obtained. The results show that the absorber containing the nanocomposite flakes with a volume fraction of 28.59% exhibits good microwave absorption properties. The reflection loss of the absorber is less than -10 dB in a frequency band of 1.93 GHz-3.20 GHz.
CoFe_2O_4 ferrite nanowire arrays are fabricated in porous silicon templates. The porous silicon templates are prepared via metal-assisted chemical etching with gold（Au） nanoparticles as the catalyst. Subsequently, CoFe_2O_4 ferrite nanowires are successfully synthesized into porous silicon templates by the sol–gel method. The magnetic hysteresis loop of nanowire array shows an isotropic feature of magnetic properties. The coercivity and squareness ratio（M_r/M_s） of ensemble nanowires are found to be 630 Oe（1 Oe = 79.5775 A·m^（-1） and 0.4 respectively. However, the first-order reversal curve（FORC） is adopted to reveal the probability density function of local magnetostatic properties（i.e., interwire interaction field and coercivity）. The FORC diagram shows an obvious distribution feature for interaction field and coercivity. The local coercivity with a value of about 1000 Oe is found to have the highest probability.
