Anisotropy magnetic properties

Substitution for Fe has a drastic effect on intrinsic magnetic properties. Partial substitution by or decreases J) without affecting seriously, resulting in larger and values. Substitution by Ti and Co causes a considerable decrease in K , the uniaxial anisotropy (if j > 0) may even change into planar anisotropy (if < 0). Intermediate magnetic stmctures are also possible. For example, preferred directions on a conical surface around the i -axis are observed for substitution (72). For a few substitutions the value is increased whereas the J) value is hardly affected, eg, substitution of Fe byRu (73) or by Fe compensated by at Ba-sites (65). 

Iron—Aluminum and Iron—Aluminum—Silicon Alloys. The influence of aluminum on the physical and magnetic properties of iron is similar to that of silicon, ie, stabilization of the bcc phase, increased resistivity, decreased ductility, and decreased saturation magnetization, magnetocrystalline anisotropy, and magnetostriction. Whereas Si—Ee alloys are well estabHshed for electrical appHcations, the aluminum—iron alloys have not been studied commercially. However, small (up to ca 0.3%) amounts of A1 have been added to the nonoriented grades of siHcon steel, because the decrease in ductiHty is less with A1 than with Si. 

The physical properties of metal nanoparticles are very size-dependent. This is clear for their magnetic properties, for which the shape anisotropy term is very important. This is also true for the optical properties of nanoparticles displaying plasmon bands in the visible range (Cu, Ag, Au) and for 111-V... 

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. 

The magnetic properties of iron oxides can be determined using Mossbauer spectroscopy, neutron powder diffraction and magnetometry (see Chap. 7). The characteristic parameters are the magnetic moment, the permeability, the saturation magnetization, the magnetic anisotropy constants and the Bhf (Tab. 6.2). 

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