J. S. van Wieringen

Magnetic properties, conductivity and ionic ordering in Fe1−xCuxCr2S4

The magnetic and electrical behaviour of Fe1−xCuxCr2S4 recently measured by Haacke and Beegle is interpreted on the basis of a model for sulphospinels given by Lotgering and Van Stapele, with the additional assumption that the Fe2+ levels are situated in the energy gap between the valence and conduction band. Experimental data supporting this interpretation are given. Ionic ordering on A-sites in Fe12Cu12Cr2S4 and ln12Cu12Cr2X4 (X = S or Se) is found by means of Mossbauer spectroscopy and X-ray diffraction.

Anisotropic Mössbauer fraction and crystal structure of BaFe 12O19

Abstract From X-ray diffraction and Mossbauer measurements on BaFe 12 O 19 single crystals it is concluded that the iron on Fe(2) sites oscillates between two positions on either side of a plane through three of its oxygen neighbours.

Note of Mössbauer fraction in powders of small particles

Abstract In powders the particles may be so small that a single particle is unable to give a “recoilless” Mossbauer transition; hence the Mossbauer fraction should depend on the degree of packing. This has been confirmed experimentally for iron oxide powders.

Study of the Mössbauer Effect, Magnetization, and Crystal Structures of the Pseudobinary Compounds ThCo5−5xFe5x and ThNi5−5xFe5x

The compounds ThCo5−5xFe5x and ThNi5−5xFe5x form two series of complete solid solutions. All compounds investigated show the hexagonal CaCu5 structure. The lattice constants, the Curie temperatures, and the saturation moments at 4.2 K have been determined as a function of x. The ThM5 compounds possess two nonequivalent crystallographic sites for the M atoms (M = Fe, Co, Ni). By means of the Mossbauer effect it is shown that the physical nature of atoms occupying these sites differs appreciably. It is also shown that replacement of Co or Ni by Fe in ThCo5 or ThNi5 proceeds with a strong preference for one of these two sites. The crystalline anisotropy of the compounds ThCo5−5xFe5x was studied as a function of x. It could be shown that the anisotropy in ThCo5 is not particularly due to one of the two Co sites. With decreasing values for x, starting from ThFe5, the Fe moment increases down to x = 0.6. This is explained in terms of a rigid‐band model.

A study of the constitution and freezing behaviour of iron oxide-hydrate gels by means of the Mössbauer effect

Abstract Iron oxide-hydrate gels, both as prepared and after subsequent freezing, have a Mossbauer absorption spectrum consisting of two peaks of equal height. The temperature dependence of the peak height can be related to the elastic properties of the gel structure and its freezing behaviour. The recoil of the absorbed gamma-radiation is taken up by the surroundings of the particles. It is concluded that the gel consists of a network of small particles (

Prospects for solar energy for providing low temperature heat

An approximate formula is derived for the average annual amount of heat produced by solar collectors in different locations. Next, a maximum price for solar installations is derived from the requirement that they should be competitive with other energy sources. Comparison with the calculated yield shows that present-day solar hot water installations will only be competitive in sunny and mild climates. In less privileged circumstances--for example, in Europe north of 45° latitude--the price of solar hot water would be too high. Even with rising energy prices this conclusion would remain valid. Cheaper collectors should therefore be developed. Because of the much lower yields in winter, solar collectors for space heating stand even less chance: they are nowhere as competitive. Passive solar systems may be the answer. It is found that Trombe walls with selective surfaces are promising and deserve further investigation.

Influence du traitement mecanique sur la résonance paramagnétique du manganese dans les poudres de sulfure de zinc

Synopsis If wurtzite, the hexagonal modification of ZnS, is compressed at room temperature, it changes into sphalerite, the cubic modification. This has been observed by X-ray diffraction 6). The gradual transition manifests itself also in the paramagnetic resonance spectrum of small quantities of Mn dissolved in ZnS (fig. 1). This is because the paramagnetic resonance spectrum of divalent manganese is very sensitive to the presence or absence of non-cubic components of the surrounding crystalline field. The spectrum as a function of Mn concentration is shown in fig. 2. In non-compressed rtzite powders the complete spectrum is resolved at higher concentrations (0.05%) than had been reported before (0.001%) 4 ) for compressed powders.

Internal magnetic fields at iron sitess in “Ticonal” permanent magnets determined by Mössbauer measurements

Abstract Mossbaue measurements sigle crystals of “Ticonal” G show that the iron in the alloy is present both in ferromagnetic and in paramagentic surroundings. After a thermal treatment the fraction of the latter typr of iorn grows while at the same time the corrective force increases.

A simple method for a fourier analysis

Synopsis A Fourier analysis has been made using only a phototension cell, an alternating current galvanometer and a rotating device.

Exact and approximate solution of the regenerator equation for the case of high heat exchange and moderate heat capacity

If the inflow temperatures are constant the regenerator equation can be transformed into an integral equation. The latter is solved numerically by an iteration procedure. From the results, a simple approximate solution is found for the case of high heat exchange (30<Λ<300) and moderate heat capacity (1.5<Γ<3).