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It is known from neutron scattering experiments that alpha-CoSO4 is a four-sublattice canted antiferromagnet with no net magnetic moment. In this paper the magnetic properties of this material are analyzed using a model in which an isotropic fictitious spin of 1/2 is assigned to each Co(++) ion. The large canting angle of 25 degrees is interpreted in terms of antisymmetric terms in the Hamiltonian due to anisotropic superexchange and the large anisotropy in the g values. Corresponding to the four sublattices, there are four spin-wave modes at k=0. Calculations indicate that the resonant frequencies of these modes should lie in the far infrared, and that only three of the modes should be observable spectroscopically. In addition, static susceptibilities of the system have been calculated for T=0 and T”Tn(12K), and the g values were estimated. Far-infrared transmission experiments resulted in the observation of three lines at 20.6, 25.4 and 35.8 cm, with relative intensities 1:1:0.1. Although these lines are presumed to be the three expected resonances, an unambiguous fitting for all the parameters of the model has not been possible. The temperature dependence of the resonance lines is anomalous. (Author).
Crystals are sometimes called 'Flowers of the Mineral Kingdom'. In addition to their great beauty, crystals and other textured materials are enormously useful in electronics, optics, acoustics and many other engineering applications. This richly illustrated text describes the underlying principles of crystal physics and chemistry, covering a wide range of topics and illustrating numerous applications in many fields of engineering using the most important materials today. Tensors, matrices, symmetry and structure-property relationships form the main subjects of the book. While tensors and matrices provide the mathematical framework for understanding anisotropy, on which the physical and chemical properties of crystals and textured materials often depend, atomistic arguments are also needed to quantify the property coefficients in various directions. The atomistic arguments are partly based on symmetry and partly on the basic physics and chemistry of materials. After introducing the point groups appropriate for single crystals, textured materials and ordered magnetic structures, the directional properties of many different materials are described: linear and nonlinear elasticity, piezoelectricity and electrostriction, magnetic phenomena, diffusion and other transport properties, and both primary and secondary ferroic behavior. With crystal optics (its roots in classical mineralogy) having become an important component of the information age, nonlinear optics is described along with the piexo-optics, magneto-optics, and analogous linear and nonlinear acoustic wave phenomena. Enantiomorphism, optical activity, and chemical anisotropy are discussed in the final chapters of the book.
This book reflects changes that have occurred during the last two decades in theoretical understanding and practical implementation of magnetic techniques in materials treatment. Research and development needs, based on the current strategic thinking and on principles of sustainable development are outlined. Development of magnetic separators based on powerful permanent magnetic materials, construction of reliable superconducting separators, design of efficient eddy-current separators and industrial implementation of magnetic carriers and magnetic fluids are examples of innovative changes that have taken place during the last twenty years. The book reflects the current technological trends and re-positions the research, development and practice of magnetic methods of material treatment in such areas as minerals beneficiation, recycling, waste treatment and biomedical and clinical applications.