Zheng Xiao-Ping

A structural, magnetostrictive and Mössbauer study of Tb0.3Dy0.7(Fe0.9T0.1)1.95 alloys

The effect of IIIA metal and transition metalT substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb0.3 Dy0.7 (Fe0.9T0.1)1.95 (T=Mn, Fe, Co, B, Al, Ga) alloys at room temperature were investigated systematically. It was found that the primary phase of the Tb0.3 Dy0.7 (Fe0.9T0.1)1.95 alloys is the MgCu2-type cubic Laves phase structure for different substitution. The magnetostrictionλs decrases greatly for the substitution of IIIA metal, B, Al and Ga, but is saturated more easily for Al and Ga substitution, showing that the Al and Ga substitution is beneficial to a decrease in the magnetocrystalline anisotropy of Tb0.3 Dy0.7 (Fe0.9T0.1)1.95 alloys. However, the substitution of transition metal Mn and Co decreases slightly the magnetostrictionλs. It was also found that the effect of different substitutions on the spontaneous magnetostrictionλ111 is distinct. The analysis of the Mössbauer spectra indicates that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry for Al and Ga substitution, namely spin reorientation, but it does not change evidently for B, Mn and Co substitution.The effect of ⅢA metal and transition metal T substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb 0.3 Dy 0.7 (Fe 0.9 T 0.1 ) 1.95 ( T = Mn, Fe, Co, B, Al, Ga) alloys at room temperature were investigated systematically. It was found that the primary phase of the Tb 0.3 Dy 0.7 (Fe 0.9 T 0.1 ) 1.95 alloys is the MgCu 2 -type cubic Laves phase structure for different substitution. The magnetostriction λ s decrases greatly for the substitution of IIIA metal B, Al and Ga, but is saturated more easily for Al and Ga substitution, showing that the Al and Ga substitution is beneficial to a decrease in the magnetocrystalline anisotropy of Tb 0.3 Dy 0.7 (Fe 0.9 T 0.1 ) 1.95 alloys. However, the substitution of transition metal Mn and Co decreases slightly the magnetostriction λ s . It was also found that the effect of different substitutions on the spontaneous magnetostriction l111 is distinct. The analysis of the Mossbauer spectra indicates that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry for Al and Ga substitution, namely spin reorientation, but it does not change evidently for B, Mn and Co substitution.

A computer simulation of nucleation and growth of thin films

A three-dimensional kinetic Monte Carlo technique has been developed for simulating the nucleation and growth of thin films. This model involves incident atom attachment, surface diffusion of the atoms on the growing surface and atom detachment from the growing surface. It takes some new effects into account, such as a significant improvement in calculation of activation energy for the atom diffusion, which renders the model more reasonable. In addition three optimum temperatures and the consistency of their dependence on deposition rate have been found out; the dependence of the surface roughness and relative density on the deposition rate has been discussed; and the approximation of freezing neighbour atoms and periodic boundary conditions has been applied.

Kinetic Monte Carlo simulation of film morphologies at the initial stages

The morphologies at the initial stages of thin film growth were studied by using Kinetic Monte Carlo techniques. A more efficient model was used to calculate the activity energy. The model involves incident atom attachment, diffusion, detachment from the surface, detached atom returning, and dimer diffusion. We edited a set of software of the model and simulated the surface morphologies by the principle of computer graphics. It is shown that the nucleuses formed at the initial stages and the surface morphologies at high temperatures are very different from those at low temperatures. The later surface growth depends on the nucleuses at the initial stages. The mechanism results from the atom thermal movement, the temperature determines the diffusion ability, and the deposition rate determines the diffusion time.