Z. D. Zhang

Enhanced natural resonance and attenuation properties in superparamagnetic graphite-coated FeNi 3 nanocapsules

Electromagnetic (EM) characteristics of superparamagnetic graphite-coated FeNi(3) nanocapsules were studied at 2-18 GHz. Compared with FeNi(3) nanoparticles coated by an amorphous oxide layer, the natural resonance and attenuation properties of the graphite-coated FeNi(3) nanocapsules were dramatically enhanced, due to the coating of the graphite. Graphite layers can restrain the growth of FeNi(3) nanocapsules, increase the resistivity, enhance the resonance frequency, keep the real part of permeability almost constant at high frequency and increase the magnetic loss. As a result of enhanced natural resonance and attenuation properties, the FeNi(3)/C nanocapsules exhibit good EM absorption properties.

Highly Transparent and Durable Superhydrophobic Hybrid Nanoporous Coatings Fabricated from Polysiloxane

Highly transparent and durable superhydrophobic hybrid nanoporous coatings with different surface roughnesses were fabricated via a simple solidification-induced phase-separation method using a liquid polysiloxane (PSO) containing SiH and SiCH═CH2 groups as precursors and methyl-terminated poly(dimethylsiloxane)s (PDMS) as porogens. Owing to the existence of SiCHn units, the hybrid material is intrinsically hydrophobic without modification with expensive fluorinated reagents. The roughness of the coating can be easily controlled at the nanometer scale by changing the viscosity of PDMS to achieve both superhydrophobicity and high transparency. The influence of surface roughness on the transparency and hydrophobicity of the coatings was investigated. The enhancement from hydrophobic to superhydrophobic with increasing surface roughness can be explained by the transition from the Wenzel state to the Cassie state. The optimum performance coating has an average transmittance higher than 85% in the visible-light range (400-780 nm), a water contact angle of 155°, and a slide angle lower than 1°. The coatings also exhibit good thermal and mechanical stability and durable superhydrophobicity, which paves the way for real applications of highly transparent superhydrophobic coatings.

Al2O3 coated α-Fe solid solution nanocapsules prepared by arc discharge

Al2O3 coated alpha-Fe solid solution nanocapsules are prepared by arc-discharging a bulk AlNiCo permanent magnet. The size of the nanocapsule is in range of 3-300 nm and the thickness of the shell is 1-6 nm. Al atoms in the AlNiCo magnet form the shell of amorphous Al2O3 to prevent the nanocapsules from further oxidation. The magnetic properties of saturation magnetization J(s) = 85 A m(2)/kg and coercive force H-j(c) = 27.5 kA/m are achieved for the nanocapsules

Direct experimental evidence for anisotropy compensation between Dy3+ and Pr3+ ions

Experimental evidence for the anisotropy compensation between Dy3+ and Pr3+ ions has been observed directly by performing x-ray diffraction on magnetic-field aligned powders and by evaluating the spin-reorientation temperature and the magnetostriction of Tb0.2Dy0.8-xPrx(Fe0.9B0.1)(1.93) alloys. The spin-reorientation temperature decreases with increasing the Pr content. The easy magnetization direction (EMD) at room temperature of the alloys rotates continuously in the (1 (1) over bar0) plane from for x=0.18 to for x=0.40, subjected to the anisotropy compensation between Dy3+ and Pr3+ ions. It is observed that the EMD of some of the alloys lies along nonmajor axes at room temperature. A maximum value of magnetostriction is achieved at x=0.22, which is also attributed to the anisotropy compensation. (c) 2006 American Institute of Physics.

CHARACTERIZATION OF FE-NI(C) NANOCAPSULES SYNTHESIZED BY ARC DISCHARGE IN METHANE

Ultrafine Fe-Ni(C) particles of various compositions were prepared by are discharge synthesis in a methane atmosphere. The particles were characterized by x-ray diffraction, transmission electron microscopy, energy disperse spectroscopy, chemical analysis, x-ray photoelectron spectroscopy, Mossbauer spectroscopy, and magnetization measurement. The carbon atoms solubilizing at interstitial sites in gamma-(Fe,Ni, C) solution particles have the effects of forming austenite structure and changing microstructures as well as magnetic properties. A carbon layer covers the surface of Fe-Ni(C) particles to form the nanocapsules and protect them from oxidization, The mechanism of forming Fe-Ni(C) nanocapsules in the methane atmosphere was analyzed.

Simple fabrication of micro/nano-porous SiOC foam from polysiloxane

Micro/nano-porous SiOC foams with narrow pore size distribution were fabricated by pyrolysis of polymeric gels prepared from mixtures of crosslinkable polysiloxane PSO and methyl-terminated polydimethylsiloxane PDMS. By simply changing the viscosity of the PDMS or its mass ratio in the mixed polymers, the pore sizes and porosities of the porous SiOC materials could be adjusted in the range from 10 nm to 3 μm, and 20% to 90%, respectively.

Effects of buffer layer and substrate temperature on the surface morphology, the domain structure and magnetic properties of c-axis-oriented Nd2Fe14B films

Anisotropic Nd-Fe-B thin films with c-axis texture are fabricated by dc magnetron sputtering on heated Si substrate. The influence of Ti or Mo buffer layer thickness and substrate temperature on the surface morphology, the domain structure and the magnetic properties are investigated and compared for the Nd-Fe-B films. It is found that the morphology of the surface strongly depends on the thickness of the buffer layer. A rough surface is observed if there is no buffer layer between the substrate and Nd-Fe-B layer or the buffer layer is too thick. Mo shows to be the better candidate for the buffer layer for its perfect lattice match with the Nd-Fe-B layer. The best values for the maximum energy products are 11.9 and 14.8 MGOe for the Nd-Fe-B films with Ti and Mo buffer layers, respectively. (c) 2005 American Institute of Physics.

Large-area, crack-free polysilazane-based photonic crystals

Large-area, crack-free inverse opal photonic crystals were successfully fabricated by conventional colloidal self-assembly method with poly(St-MMA-AA) as the opal template and a thermosetting polysilazane as the infiltrating polymer. The phenomenon of self-healing of cracks in the opal template was observed and attributed to the unique rheology property of the used polysilazane. Under an optimized pyrolysis condition, a hybrid inverse opal photonic crystal with its refractive index at 2.21, filling fraction of the solid material at 0.66, and area around 8 mm × 10 mm was prepared.

Large low-field inverse magnetocaloric effect in Ni 50−x Mn 38+x Sb 12 alloys

The magnetic properties and magnetocaloric effects of Ni(50-x)Mn(38+x)Sb(12) ferromagnetic shape-memory alloys with x = -1, 0, 1 and 2 that undergo a martensitic transformation were investigated. The magnetic-entropy changes Delta S of nominal Ni(49)Mn(39)Sb(12), or Ni(49.5)Mn(38.6)Sb(11.9), at 279K is 6.15 J kg(-1) K(-1) for a magnetic-field change Delta B = 1 T, with negligible hysteresis loss, as it transforms from a low-temperature martensitic phase to a high-temperature austenitic one. The large inverse Delta S in a small field change and the negligible hysteresis loss, along with the low cost of Sb, indicate that Ni(49)Mn(39)Sb(12) is a promising candidate for room-temperature magnetic refrigeration.

Unconventional exchange bias in CoCr2O4/Cr2O3 nanocomposites

Unconventional exchange bias (EB) has been studied in CoCr(2)O(4)/Cr(2)O(3) nanocomposites, in which the Curie temperature of the ferrimagnetic CoCr(2)O(4) is much lower than the Neel temperature of the antiferromagnetic Cr(2)O(3). A negative EB field of about 2.5 kOe at 5 K is achieved upon cooling in a field of 30 kOe. Meanwhile, the coercivity of the CoCr(2)O(4) nanoparticles has been enhanced significantly by coupling with Cr(2)O(3). The effect of the cooling field on the EB field and coercivity at 10 K has also been investigated. The domain-state model is used to interpret the unconventional EB. Cooling field may play a decisive role in the creation of the interfacial spin configuration for the unconventional EB, not only by exchange interaction between the induced magnetization of a polarized paramagnet and interfacial spins of an antiferromagnet but also by Zeeman interaction between the domain-state surplus magnetization and the external field.