Anisotropy in the magnetic properties

Such a behavior suggests, above TN, a description of the material in terms of discrete units. Clearly, the proposed model does explain the absence of significant anisotropy in spite of the local distortion at each site and the exchange contribution. In such examples, the distortions from the Oh symmetry constitute generally the driving force and lead to a high anisotropy of the magnetic properties. In fact, we have to describe here an unusual situation, in that the... 

Bellot et al. (1992) have studied this compound by the °Yb Mossbauer spectroscopy method and have carried out magnetization measurements on a single crystal. It was found that the Curie point is equal to 5.65 K. There is a strong anisotropy of the magnetic properties in different crystallographic directions. The magnetic moment of Yb lies along... 

Gibson and Putzer prepared Co platelet particles by sonicating an aqueous Co solution in the presence of hydrazine (141). The Co particles thus obtained were essentially hexagonal, about 100 nm wide, and 15 nm thick (Figure 16). An interesting issue with these particles was the shape-property relationships, such as the potential effects of shape anisotropy on the magnetic properties of the particles. 

The anisotropy in the magnetic susceptibility like that in other prc orties depends not only on the major order parameter but also on the biaxiality parameter (Sxx - S y). We shall consider the likely magnitude of this new contribution in the final section. The converse of the result in EQN (41) is that measurement of the anisotropy in a single property is clearly insufficient to determine the two order parameters even if the principal axes are known. 

To appreciate the significance of these numerous orda parameters it is helpful to see how they are related to the anisotropic properties of a nematic. As an example we consider the anisotropy in the magnetic susceptibility. Ax, as we have for previous systems. The starting point is the magnetic polarisability expressed in a molecular frame s in a rigid fragment of the molecule. This tensor K ( ends, in genaal, on the conformation of the molecule, a fact which we have... 

Tellurium also improves the properties of electrical steels by aiding in the magnetic anisotropy, malleable cast iron (77), and spheroidal (graphitic) cast irons (see also Metal surface TiiEATiffiNTs). 

With respect to the physical properties mentioned, band-structure calculations have attracted considerable interest, e.g., for SbSBr, SbSI, and SbSel (234). For the compounds having reference 22i in column 4 of Table XXIX, a temperature-independent diamagnetism has been found, with values of about 10 cm" g between 77 and 340 K. A small temperature-dependence is exhibited by BiTel, a narrow-gap semiconductor (41). The anisotropy of the magnetic susceptibility has been studied for SbSI, BiSel, and BiTel (41, 420). 

Mirzamaani et al. [74, 75] point out that the earlier studies of the interrelationships between structure and magnetics have examined films substantially thicker than those now being used in thin-film disks. These authors have examined very thin CoP films and have studied the relative roles of shape anisotropy, stress anisotropy, and crystal anisotropy in determining the magnetic properties. For their CoP-deposition system, shape anisotropy dominated the other factors in determining the film magnetic properties. The shape anisotropy of a particular deposit was determined by the surface condition of the substrate on which the CoP was deposited. 

The structures of electroplated hard alloys have been less extensively studied than those of similar electrolessly deposited materials. Sallo and co-workers [118-120] have investigated the relationship between the structure and the magnetic properties of CoP and CoNiP electrodeposits. The structures and domain patterns were different for deposits with different ranges of coercivity. The lower-f/c materials formed lamellar structures with the easy axis of magnetization in the plane of the film. The high-Hc deposits, on the other hand, had a rod-like structure, and shape anisotropy may have contributed to the high coercivity. The platelets and rods are presumed to be isolated by a thin layer of a nonmagnetic material. 

Crystals in which the molecules are all parallel to each other have the same characteristics as the individual molecules. But when there are two or more differently oriented molecules in the unit cell, the magnetic anisotropies of the individual molecules are to some extent neutralized. The magnetic properties of a crystal are, very precisely, the vectorial sum of those of the constituent molecules. (Foi equations, see Lonsdale,... 

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