Xianguo Liu

Magnetocaloric effect and magnetic-field-induced shape recovery effect at room temperature in ferromagnetic Heusler alloy Ni?Mn?Sb

The martensitic transition, magnetocaloric effect ( MCE) and shape memory effect ( MSE) of ferromagnetic Heusler alloys Ni50Mn50-x Sb-x (x = 12, 13 and 14) have been investigated. A large positive magnetic entropy change Delta SM was observed in the vicinity of the martensitic transition. The maximum value of Delta SM is 9.1 J kg(-1) K-1 in Ni50Mn37Sb13 at 287K for a magnetic field change of 5 T. This change originates from the first-order transition from a low-temperature weak-magnetic martensitic phase to a high-temperature ferromagnetic parent phase. A magnetic-field-induced shape recovery strain of about 15 ppm at room temperature and at a relatively low magnetic field ( 1.2 T) was observed to accompany the reverse martensitic transformation. The large field-induced MCE and MSE in the NiMnSb system make it a promising material for room-temperature application.

Microwave-absorption properties of Fe(Mn)/ferrite nanocapsules

Electromagnetic ( EM) wave absorption properties of the paraffin-Fe(Mn)/ferrite nanocapsule composite ( with 40 wt% nanocapsules) were investigated in the 2-18 GHz frequency range. The Fe(Mn)/ferrite nanocapsules synthesized by arc-discharging have a core-shell structure with cores 10-30 nm in diameter and shells about 5 nm in thickness. The reflection loss (RL) calculated from the measured permittivity and permeability was found to exceed -20 dB in the 13-15 GHz range for a thickness of about 1.75-1.95 mm. The optimal RL is -28.2 dB at about 14 GHz with 1.84mm thickness. RL values exceeding -10 dB were obtained for the absorber of 1.7mm thickness in the range 12.7-17.1 GHz, which almost covered the whole Ku-band (12.4-18 GHz). The excellent EM wave absorption properties of the Fe(Mn)/ferrite nanocapsules significantly depend on the core-shell microstructure and the match of dielectric and magnetic losses.

Fluorescence and microwave-absorption properties of multi-functional ZnO-coated α-Fe solid-solution nanocapsules

Fluorescence (FL) and microwave-absorption properties of multi-functional α-Fe solid-solution nanocapsules have been investigated. High-resolution transmission electron microscopy and x-ray photoelectron spectroscopy analysis show that the nanocapsules have a shell/core structure with α-Fe solid-solution nanoparticles as the core and amorphous ZnO as the shell. The nanocapsules are ferromagnetic at room temperature. There is a tendency to redshift for the peak at 388 nm in the FL spectra as the Zn concentration decreases. The in-depth study of relative permittivity and permeability reveals that the ZnO-coated α-Fe solid-solution nanocapsules exhibit excellent microwave-absorption properties, because of a proper electromagnetic match in the microstructure, strong natural resonances and dipolar polarization mechanisms.

Magnetic and Microwave-absorption Properties of Graphite-coated (Fe, Ni) Nanocapsules

The structure, magnetic and microwave-absorption properties of graphite-coated (Fe, Ni) alloy nanocapsules, synthesized by the arc-discharge method, have been studied. High-resolution transmission electron microscopy shows that the nanocapsules have a core/shell structure with (Fe, Ni) alloy as the core and graphite as the shell. All (Fe, Ni) alloy nanocapsules/paraffin composites show good microwave-absorption properties. The optimal reflection loss (RL) was found for (Fe(70)Ni(30))/C nanocapsules/paraffin composites, being -47.84 dB at 14.6 GHz for an absorber thickness of 1.99 mm, while the RL values exceeding -10 dB were found in the 12.4-17.4 GHz range, which almost covers the K(u) band (12.4-18 GHz). For (Fe(70)Ni(30))/C nanocapsules/paraffin composites, RL values can exceed -10 dB in the 11.4-18 GHz range with an absorber thickness of 1.91 mm, which cover the whole K(u) band.