Franklin F.Y. Wang

Magnetic ordering in Ba2MnReO6

Abstract The ordered perovskite Ba 2 MnReO 6 has been reported to be ferrimagnetic with a Curie temperature of 105°K and a saturation moment of 3.9 μ B , consistent with antiparallel coupling of spin-only moments of the combination Mn 2+ Re 6+ . Neutron diffraction studies on polycrystalline material have confirmed that the Mn and Re ions are completely ordered chemically. At 4.6°K, two sets of magnetic peaks were observed, the stronger consistent with the ferrimagnetic model, and the weaker characteristic of antiferromagnetic ordering of the first kind, indicative of some canting of the moments in adjacent (001) planes. The moment on the Mn ion was found to be 4.8μ B , but that on the Re ion was found to be less than 0.2 μ B if a localized free-ion form factor is assumed. These results can be interpreted in terms of an extended spin density distribution due to covalent bonding in the ReO 6 clusters.

Fracture surface energy determination in {1 1 0} planes in silicon by the double torsion method

The fracture surface energy of {110} planes of silicon were determined by the double torsion method on thin samples. Elastic anisotropy was taken into account in the calculations. The determined value of 1.81 J m−2 compared well with other data in the literature.

Effect of gadolinium substitution on the linear thermal expansion of barium sodium niobate

Abstract Ba2NaNb5O15 (BSN) exhibits a large thermal contraction in its c-axis between 350° and 750°C. This behaviour contributes to a serious cracking problem during its crystal growth. The substitutions of Gd for Ba and/or Na in BSN can be made with either anion or cation compensation. The former, namely, type A, compositions were found to eliminate the thermal contraction behaviors, and had small variations in their linear thermal expansion coefficients, α, between 50° and 650°C. With good ferroelectric and dielectric properties, they showed potentials to replace the BSN crystal in electro-optic devices.

Phase transformation in the oxides

This paper reviews phase transformations in the oxides, and briefly examines the similarities and dissimilarities with the phase transitions in metals. A few topics selected for the discussion, include, displacive phase transitions, order-disorder transitions, and clustering and precipitation. The displacive transition involves the oxygen polyhedra, and is usually found in ferroelectric and antiferroelectric oxides, such as, BaTiO3, SrTiO3, PbZrO3, and other oxides of perovskite structure. In lattice dynamics studies, this transition has been associated with an instability of a long-wave optical phonon. The condensation of the ferroelectric soft mode causes the static distortion of the lattice at the phase transition. The order-disorder transformation in the oxides may occur in different forms. It may be the hydrogen ordering in KDP, the catio distributions in spinel MgFe2O4,the Li-Fe ordering of the octahedral sites in LiFe5O8, or the formations of layer structures in the double perovskites, such as Ba2CoWO6, Ba2CoReO6, and others. Clustering and precipitations are commonly observed phenomena in oxide systems. They result in phase separations in both the crystalline, and the glassy systems. Heat treatments to control the crystallization processes in glasses result in glass ceramics, which have been proven to be superior to both the original glass, and to the precipitated crystalline phase.

Calculation of the elastic moduli of binary composites

Abstract A modification was introduced to Hashin and Shtrikmans variational approach to calculate the elastic moduli of binary composites. The distribution effect of dispersed phases was taken into account. As a first approximation, a normal distribution was assumed. The calculations of moduli of nine systems were compared with the results of experiments for concentrations up to 50%. The introduction of a distribution effect showed distinct improvement.

The magnetic structure of Ba2MnWO6

Powder neutron diffraction and magnetic measurements have shown that the ordered perovskite Ba2MnWO6 is antiferromagnetic with a Neel temperature of 7.5 ± 1°K. Below this temperature, ordering of the second kind occurs, with the Mn moments directed perpendicular to the [111] axis.

Refinements in the determination of minority-carrier diffusion length measurements of polycrystalline silicon materials by the surface photovoltage method

The microstructures of polycrystalline silicon samples show significant differences in their absorption coefficients within the range of wavelength of interest for the surface photovoltage (SPV) method. The accuracy in the determination of the minority‐carrier diffusion length of polycrystalline materials by the SPV method was demonstrably improved with the use of the determined absorption coefficients for each individual sample.

Synchrotron X-ray topographic studies of the changes in defect microstructure induced by rapid thermal processing of single-crystal silicon wafers

Abstract Synchrotron white beam X-ray diffraction topography in transmission geometry has been used to non-destructively investigate defect structures in silicon single-crystal wafers, both prior and subsequent to a 60 s rapid thermal processing (RTP) treatment at 1050°C. Among the effects observed were: dislocation glide and multiplication; and the enhancement of the strain field associated with A-type swirl defects.

Two‐Dimensional Stress Measurement in Permalloy Thin Films by Moiré Method

A modified Ligtenbergs reflective Moire method may be used to measure stress in Permalloy film (∼1000 A) on glass substrate. At four points on a sample film, stress values ranged between 109 and 1011 dyn/cm2. Angle φ between the principal stress S1 and the x axis varied from 178.5° to 0°. The extent of such variations differed with each individual film on substrate. Their causes were not determined in this study. This Moire technique can be very useful in establishing these causes.

Transition Layers between Magnetic Domains

A new approach is introduced to study the transition layer between magnetic domains in magnetic films. The approach is to approximate the spin configuration in a transition layer by a generalized functional form of a spiral. The equilibrium wall energy and wall thickness can be obtained by the minimization of the total energy. For each prototype of domain wall, the cone angle of the spiral provides an additional variable parameter. External conditions such as imperfections and grain boundaries can cause the spin configuration to assume a different cone angle. A phase diagram of minimum energy 180° Neel wall spin configurations is given.