Single-domain particle diameter

Domain-wall surface energy y, domain-wall width W, single-domain particle diameter Dc, average width of the domain Z) and grain diameter Da in various permanent magnet materials. 

Numerical values obtained by various authors in several magnetic materials of interest can be compared in table 15. It follows from these data that the single-domain particle diameter Dc is smaller than the grain diameter DG in sintered... 

We now focus on a ferrofluid of single-domain particles of the amorphous alloy Fei cC c (x 0.2-0.3). The particles were coated with a surfactant (oleic acid) and dispersed in a carrier hquid (xylene). The particle shape is nearly spherical (see Fig 3.14) and the average particle diameter d = 5.3 0.3nm. The... 

In Figure 13 the relation between the intrinsic coercivity Ha and the particle diameter dis given. The figure is based on a described model (35). The maximum is found around the critical particle diameter. In general the particle diameter and size is not very well defined. For the multidomain particles (d > dcritical ) the Ha is smaller than the intrinsic anisotropy field of the particle. Nucleation effects cause a decrease in FF. as the d increases. This behavior is understood only qualitatively for a full description see Reference 36. Low noise media should consist of single-domain particles reversal by domain walls is slow and introduces noise. 

The sintered Nd-Fe-B magnets have the grain size spin melting have = 200-800 A. Since the critical diameter for single domain particles is —0.3 /im, in the first case the particles are greater while in the second one are smaller than the critical size (Livingston 1985b)... 

BaTiC>3 particles are another very attractive and intensively studied type of nanoparticles in nematic liquid crystals. Cook et al. reported on an asymmetric Freedericksz transition, where doping nematic TL205 with single domain ferroelectric BaTiC>3 nanoparticles (9 nm in diameter) reduced or increased the threshold voltage by 0.8 V depending on the polarity of the applied voltage [149]. 

Figure 5 Effect of grid resolution (A.) on the time-averaged dimensionless slip velocity (us/uT). Geldart group A particles are used. The ordinate is scaled with the terminal velocity of single particles (uT 21.84 cm/s) and the abscissa is scaled with the particle diameter dp. The domain size is 1.5 x 6 cm2, comparable to the coarse-grid used in normal simulations.

A total of 1500 crystallites and 500 particles was assumed for the calculations. The particles were randomly oriented. The anisotropy constant of the crystallites was Kt = 5.6 106 J/m3, Js = 1.31 [28]. The exchange constant was varied in the range of A = 0.1 10 11 J/m to A = 2.2 10 uJ/m. Five percent of all crystallites are assumed to remain in the disordered fee phase. To represent the fee phase we simply set Ki = 0. For the chosen parameters the critical size for magnetization reversal by uniform rotation, dcrit, is in the range from 7.8 to 36 nm which is greater than the assumed particle diameter of 5 nm. For comparison, the critical single domain diameter, D, is in the range from 130 to 590 nm. 

Under the size reduction of small magnetic particle a critical volume exists when the energy to produce a domain wall becomes higher than the external magnetostatic energy for the single-domain state. This critical size depends on type of magnetic material and is about few tens nanometers. For a spherical particle, this critical diameter could be estimated as [1] ... 

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