Size Effect Parameters Research Articles

SHORT RANGE ORDER IN Ni–Nb ALLOY

Diffuse X-ray scattering intensity was measured in polycrystalline samples of Ni–Nb system. From this diffuse scattering intensity, short-range order parameters and size effect parameters were calculated. The absolute value of short-range order parameters suggest a local order present in this alloy. The ordering potential was calculated on the basis of the statistical pseudopotential theory of ordering and it was found that the calculations take into account the experimentally observed sign of the short-range order parameters.

A note of the fundamental dynamical flow characteristics of magnetic fluids. Comparison between simple shear and constant pressure gradient flows.

When a homogeneous magnetic field is applied parellel to the flow direction, physical quantities such as velocity, angular velocities of fluid and suspended particles, shear stress and pressure are theoretically obtained for two fundamental magnetic fluid flows i.e., a simple shear flow and a constant pressure gradient flow between two parallel plates, under the consideration of the diffusion effect of internal angular momentum on the basis of governing equations for a magnetic fluid, in which is used the constitutive equuation of magnetization proposed by the authors in the previous report. The fundamental dynamical flow characteristics of a magnetic fluid are comprehensively clarified by investigation of the differences which some dimensionless numbers (micropolar effect parameter, magnetic effect parameter, size effect parameter and so on) have on these two kinds of flow. Furthermore a limit of range for the wall surface coefficient when the applied magnetic fields exist is given.

The effects of oxygen on quenched-in resistivity measurements of copper

A quenching apparatus was built in which the gaseous environment could be controlled to an oxygen partial pressure of less than 10-14 Pa, in order to examine the effect of oxygen on the quenched-in resistivity, Delta rho Q, of thin, high-purity, copper samples. Oxygen was found to significantly affect measurements of Delta rho Q through internal oxidation of magnetic impurities, through precipitate formation and through changes of the size-effect parameters (surface specularity and bulk mean free path of the electron). The complex interaction of these effects of oxygen on the quenched-in resistivity of copper samples is discussed.

Electric field gradient in copper alloys

The electric field gradient q and asymmetry parameter eta are calculated for non-magnetic dilute copper alloys. Both the valence and size-effect contributions are evaluated explicitly. The transition metal model potential theory is used to evaluate the contribution from the valence effect. The formalism due to Sagalyn and Alexander (1977) is adopted to evaluate the size-effect contribution. Only the size-effect parameter lambda is introduced to explain q and eta , whose calculated values are found to be in close agreement with the experimental values. The effective hardness of fourth row impurities is found to be larger than that of the fifth row impurities. The magnitudes of q and eta are found to be proportional to the effective charges on impurities if the evaluation of these charges includes both the size effect and bound state.

Fundamental Steady F1ow of Polar Fluids

A few fundamental steady flows of polar fluid, i.e., flow in a circular tube, flow between two parallel plates and flow between two ooaxial cylinders are analysed with the help of the theory of Eringen. Couple stress and spin angular momentum are considered in this approach. The exact solutions for velocity, micro-rotation, vortioity and shearing stress are obtained mathematically. These solutions are characterized by two parameters, i.e., the ratio of viscosities e and the size effect parameter λ which do not appear in a Newtonian fluid. e is the ratio of vortex visoosity to shear viscosity. λ means the size relation between the corpuscle and the characteristic length. The solutions are compared with those of Newtonian fluid and it is investigated how they vary with e and λ. Apparent viscosity is determined for each flow. Material constants of polar fluid can be decided from these apparent viscosities.

Density of states and spin susceptibility of a finite metal: Normal and giant surface effects

The size effect on the electronic density of states and spin susceptibility $\ensuremath{\chi}$ of small metal particles and thin films is evaluated to order (area/volume) within the spin-density functional formalism. Conditions are given under which the size effect arises only in the surface region. Size-effect parameters and magnetization profiles, as well as surface energies and work functions, are calculated self-consistently for the jellium surface using the random-phase approximation and the local spin-density approximation (LSDA) for exchange and correlation. The jellium surface is also used to test two approximations for $\ensuremath{\chi}$ which require only spin-unpolarized calculations. One of them, the Vosko-Perdew (VP) approximation, is found to agree closely with the full spin-polarized calculation within the LSDA. The VP theory, which gives lower bounds for the bulk and surface susceptibilities and does not necessarily require the LSDA, is used to discuss the possibility of a giant surface effect, i.e., a giant enhancement of the surface susceptibility, in any metal that is nearly ferromagnetic. The giant surface effect is illustrated by an LSDA calculation for a low-density jellium, and by two other instructive models.

The characterization of annealing in thin metal films using the Mayadas-Shatzkes theory

A technique suggested by Mola and Heras of analyzing thin film size effect data is used to characterize the structure of thin polycrystalline metal films. A linear least-squares analysis of the product of resistivity and thickness versus thickness allows a consistent determination of the size effect parameter α. Annealing studies (130–460 K) on gold films (120–1150 Å) yield temperature-independent values of the reflection coefficient both before and after annealing and allow the annealing to be characterized quantitatively.

An X-ray diffuse scattering study of short-range order in CuAu

The diffuse X-ray scattering has been measured from a CuAu single crystal held at 700 and 800 K and from a crystal quenched from 1070 K and held at room temperature and 126 K. The short-range order and size effect parameters were calculated by use of the appropriate Fourier transforms. The order parameters obtained indicate that with increasing temperature the short-range order both decreases in magnitude and damps out faster with increasing co-ordination shell number. A calculation of the diffuse intensity using the Clapp-Moss pair correlation theory reveals that the interatomic potential ratios V 2 V 1 and V 3 V 1 are not sufficient to reproduce the experimental results but inclusion of V 4 V 1 and V 5 V 1 greatly improves the simulation. The values of V i V 1 used fit the form of a long-range oscillatory potential. Computer simulation of the atomic arrangement shows the existence of small ordered regions in a random matrix above T c but for the quenched state a microdomain structure is predicted.

Long-range and short-range order in NiPt

Experimental measurements were performed on a 48.4 at. % Ni/51.6 at. % Pt alloy. The order parameter S in equilibrium was measured as a function of temperature T by means of X-ray diffraction. Up to 592±3°C the sample is a single-phase ordered alloy with an order parameter above 0.98. Between 592 and 625±3°C there exists a two-phase region in which the ordered and disordered phases are in equilibrium. Above 625±3°C a disordered f.c.c. structure exists. Diffuse X-ray intensity measurements were performed at T = 1.1 Tc and both the short-range parameters αi and the size-effect parameters βi were calculated. From the αi parameters so derived three ordering energies νi were determined. It was found that these energies were consistent with the symmetry of the ordered phase below the critical temperature.

ORIGIN OF THE ELECTRIC FIELD EFFECT IN SILVER

The electric field effect of epitaxial silver films on mica in vacuum is studied as a function of temperature, thickness, and surface specularity. Using size-effect parameters derived from the analysis of film resistivity, the data indicate that the predominant mechanism for altering the thin-film conductance is the change in surface scattering due to surface charging of the interface.

Détermination des coefficients d'ordre à courte distance de solutions solides polycristallines. Comparaison de deux techniques d'analyse mathématique du profil d'intensité des rayons X diffusés

Two distinct methods are used for scaling the diffuse scattering. The first short-range-order coefficients αi and the first size-effect parameter β1, are derived from data on the stoichiometric CdMg3 alloy by means of two mathematical analyses which are then compared: a modified Fourier transform and a method minimizing the sum of the squares with linear constraints.