Chen Nan-xian

Algebraic rings of integers and some 2D lattice problems in physics

This paper develops the Mobius inversion formula for the Gaussian integers and Eisensteins integers, and gives two applications. The first application is to the two-dimensional arithmetic Fourier transform (AFT), which is suitable for parallel processing. The second application is to two-dimensional inverse lattice problems, and is illustrated with the recovery of interatomic potentials from the cohesive energy for monolayer graphite. The paper demonstrates the potential application in the physical science of integral domains other than the standard integers.

Structural and Thermodynamic Properties of M3W3N (M = Fe, Co, Ni)

Ternary transition metal nitrides, Fe3 W3N, Co3 W3N, and Ni3 W3N, are studied by the use of interatomic potentials acquired from lattice inversion. The study indicates that Fe3 W3N would be more stable than the other compounds in the family of intermetallic tungsten nitrides. The investigation of phonon density of states indicates that the lower frequency modes are mostly excited by the metal atoms, and the higher frequency modes are mostly excited by the nitrogen atoms. A qualitative analysis is carried out with the relevant potentials for the phase stability and vibrational modes.

Structure and magnetic properties of (Nd1?xErx)3Fe25Cr4.0 (0 ? x ? 0.8) compounds

The structure and magnetic properties of (Nd1-xErx)(3)Fe25Cr4.0 compounds with x = 0-0.8 have been investigated using x-ray powder diffraction (XRD) and magnetic measurements. It has been found that all the compounds crystallize in a Nd-3(Fe,Ti)(29)-type structure. Substitution of Er for Nd leads to a contraction of the unit-cell volume. The Curie temperature, T, and the saturation magnetization, M-s, of (Nd1-xErx)(3)Fe25Cr4.0 decrease monotonically with increasing Er content. The easy magnetization direction (EMD) of Nd3Fe25Cr4.0 at room temperature is close to the [040] direction but may be a little out of the basal plane. With increasing Er content, the EMD changes closer to the [40-2] direction and the tilt angle increases. Both the XRD patterns and ac susceptibility indicate the appearance of a spin reorientation for x = 0-0.4 as the temperature decreases from room temperature to 77 K. The spin reorientation temperature, T-sr, increases monotonically with increasing Er content from 158 K for x = 0 to 198 K for x = 0.4. A first order magnetization process (FOMP) occurs for all the compounds, and the critical field of the FOMP decreases with increasing Er content from 6.6 T for x = 0 to 2.0 T for x = 0.7.

NEAR-RESONANT RAMAN-SCATTERING FROM GAAS/ALAS SUPERLATTICES

The outstanding hard-magnetic properties are reported of Sm3Fe28.1-xCoxMo0.9 compounds with x=12, 14, 16. In this alloy system, only a small amount of Mo is needed to stabilize the 3:29 structure so that the magnetic properties are not seriously affected by the presence of this nonmagnetic element. Substitution of Co for Fe leads to a significant increase of the magnetic anisotropy, and for x greater than or equal to 14 the easy magnetization direction changes from easy plane to the easy axis. In this alloy system, the compound Sm3Fe12.1Co16Mo0.9 is a very promising candidate for permanent magnet applications. Its room temperature saturation magnetization (mu(0)M(s)=1.5T) and anisotropy field (B-an=6.5 T) are comparable to the values for Nd2Fe14B (mu(0)M(s)=1.6 T and B-an=7 T). However, the Curie temperature of Sm3Fe12.1Co16Mo0.9 is 1020 K, which is appreciably higher than that for Nd2Fe14B (T-C=588 K).

Structure Properties of Ternary Hydrides Ni3AlHx

The structure properties of the ternary hydrides Ni3AlHx are studied by use of the interatomic pair potentials obtained from the first principles electronic structure calculation and Chen-Mobius 3-dimensional lattice inversion method. The heat of formation and volume expansion of the hydrogenized systems are investigated.

Determination of Hydrogen Activation Energy Spectrum in Amorphous Solids from Internal Frictions

It is shown that the activation energy spectrum of hydrogen in amorphous materials can be determined from the temperature distribution of internal friction observed in anelastic relaxation measurements by using the deconvolution method of Fourier transform.

Modified Carlsson-Gelatt-Ehrenreich Scheme for the Inverse Problem of Cohesive Energy

By using the Hardy-Wright-M?bius inverse formula, we have improved the Carlsson-Gelatt-Ehrenreich scheme for the inverse problem of cohesive energy. The advantage of the new method is that the inverse formula are in a sense independent of the geometries of lattices.