Effect of fabrication parameters on the microstructure,in-plane anisotropy and magnetostriction of Fe-Ga thin films

The microstructure,in-plane anisotropy,and magnetic properties of Fe-Ga thin films were investigated by X-ray diffraction analysis,vibrating sample magnetometer,and capacitive cantilever method.The in-plane induced anisotropy is well formed by the applied magnetic field during sputtering,and the anisotropy field Hk decreases with the sputtering power increasing.The coercivity of Fe-Ga thin films decreases with increasing power when the sputtering power is less than 60 W and increases when the power is larger than 60 W.The magnetostriction of the thin films reaches 66 × 10-6 at the sputtering power of 60 W.Excellent Fe-Ga films,which exhibit good field sensitivity,low coercivity and high magnetostriction,have been fabricated at the power of 60 W,and they can be used as the materials of magnetostrictive transducers.

An Inverse Approach for Extracting Elastic-plastic Properties of Thin Films from Small Scale Sharp Indentation

An inverse method for extracting the elastic-plastic properties of metallic thin films from instrumented sharp indentation has been proposed in terms of dimensional analysis and finite element modeling. A wide range of materials with different elastic modulus, yield strength, and strain-hardening exponent were examined.Similar to the Nix-Gao model for the depth dependence of hardness H,the relationship between elastic modulus E and indentation depth h can be expressed as By combiningthese two formulas, we find that there is a relationship between yield stress and indentation depth h：where σyO is the yield strength associated with the strain-hardening exponent n, the true hardness Ho and the true elastic modulus Eo.is constant, whichis only related to n, and hH and hE are characteristic lengths for hardness and elastic modulus. The results obtained from inverse analysis show that the elastic-plastic properties of thin films can be uniquely extracted from the solution of this relationship when the indentation size effect has to be taken into account.

Plasma-enhanced atomic layer deposition of Co using Co(MeCp)_2 precursor

Cobalt （Co） thermal or plasma enhanced atomic layer deposition （PE-ALD） was investigated using a novel metal organic precursor, Co（MeCp）2, and NH3 or H2 or their plasma as a reactant. The growth characteristics, electrical and microstructural properties were investigated. Especially, PE-ALD produced Co thin films at low growth temperature down to 100℃. Interestingly, the low temperature growth of Co films showed the formation of columnar structure at substrate temperature below 300℃. The growth characteristics and films properties of PE-ALD Co using bis（η-methylcyclopentadienyl） Co（II） （Co（MeCp）2） was compared with those of PE-ALD Co using other Cp based metal organic precursors, bis-cyclopentadienyl cobalt （II） （CoCp2） and cyclopentadienyl isopropyl acetamidinato-cobalt （Co（CpAMD））.

Microwave magnetic properties of soft magnetic thin films

We review our works that focus on the microwave magnetic properties of metallic, ferrite and granular thin films. Soft magnetic material with large permeability and low energy loss in the GHz range is a challenge for the inforcom technologies. GHz magnetic properties of the soft magnetic thin films with in-plane anisotropy were investigated. It is found that several hundreds of permeability at the GHz frequency was achieved for Col00_xZrx and Co90Nbl0 metallic thin films because of their high satu- ration magnetization, and an adjustable resonance frequency from 1.3 to 4.9 GHz was obtained. Compared with the metallic thin films, the weaker saturation magnetization of Ni-Zn ferrite thin films results in several tens of permeability at the GHz frequency, but the larger resistivity of the ferrite prepared in situ without any heating treatments has lower energy loss. In order to obtain materials with large permeability and low energy loss in the GHz range, the [CoFe-NiZn ferrite] composite granular thin films were investigated, where the advantage of higher saturation magnetization for the metallic alloy and the high resis- tivity as well as high saturation magnetization for the ferrite results in a good GHz magnetic performance.

Mobility and sulfidization of heavy metals in sediments of a shallow eutrophic lake, Lake Taihu, China

The technique of DGT（diffusive gradients in thin films） using three diffusive gel thicknesses was applied to estimate the mobility and bioavailability of heavy metals in sediments and porewater of Lake Taihu, China. The DGT results showed significantly positive correlations between Co, Pb, Cd and Mn, and Ni and Fe concentrations in porewater. Cu and Zn showed a significantly negative correlation with Mn, due to Cu combination with carbonates and Zn derived from agricultural pollution, respectively. The rank order of average concentrations of Co, Ni and Cd at each station was DGT1.92〉DGT0.78〉 DGT0.39, suggesting stronger resupply from sediments to porewater when using thicker diffusive gels. Comparing centrifugation and DGT measurements, Co, Ni and Cd are highly labile; Mn and Fe are moderately labile; and Cu, Zn and Pb are slightly labile. The variations of AVS concentrations in sediment cores indicate that metal sulfides in deeper layers are easily diffused into surface sediments.

Tailoring mechanical heterogeneity,nanoscale creep deformation and optical properties of nanostructured Zr-based metallic glass

Metallic glasses are spatially heterogeneous at the nanometer scale.However,the effects of external excitation on their structural and mechanical heterogeneity and the correlation to their properties are still unresolved.Nanoindentation,atomic force microscopy(AFM) and high-resolution transmis sion elec tron micro scopy(HRTEM) were carried out to explore the effects of cryogenic thermal cycling(CTC) on mechanical/structural heterogeneity,nano sc ale creep deformation and optical properties of nano structured metallic glass thin films(MGTFs).The results indicate that CTC treatment alters the distribution fluctuations of hardness/modulus and energy dissipation and results in an increase-then-decrease variation in mechanical heterogeneity.By applying Maxwell-Voigt model,it can be shown that CTC treatment results in a remarkable activation of more defects with longer relaxation time in soft regions but has only a slight effect on defects in hard regions.In addition,CTC treatment increases the transition time from primary-state stage to steady-state stage during creep deformation.The enhanced optical reflectivity of the MGTFs after 15 thermal cycles can be attributed to increased aggregation of Cu and Ni elements.The results of this study shed new light on understanding mechanical/structural heterogeneity and its influence on nanoscale creep deformation and optical characteristics of nanostructured MGTFs,and facilitate the design of high-performance nanostructured MGTFs.