Dipolar magnetic particles

Figure 4.39 Dipolar chains formed by magnetic particles, (a) A semi-flexible chain of magnetic particles showing the head-to-tail, paired dipoles in the middle section and the unpaired dipoles at the ends (b) A self-...

Pastor-Satorras R, Rubi J (2000) Dipolar interactions induced order in assemblies of magnetic particles. J Magn Magn Mater 221 124—131... 

In conclusion, FMR experiments represent a useful tool for studying the dynamical behavior of fine magnetic particles and for obtaining information on the anisotropy energy and on the orientational distribution of easy axes. The proposed theoretical models are able to fit qualitatively the experimental spectra. However some important aspects, strongly affecting the thermal fluctuations of particle moments, have not yet been accounted for, for example, the effect of dipolar interactions in dynamical conditions (the dipolar local fields fluctuate in time in a system of nonidentical particles) and the effect of surface layers. Moreover, some models are valid only if H and cannot be applied when H is small. 

The significant facts of the dipolar interaction are that (i) it is a many-body interaction, (ii) it occurs between all magnetic particles in the sample, and (iii) it is a second-rank tensor interaction, i.e., is anisotropic with terms such as (l-3cos 0j ) featuring in it. For spin 1/2 nuclei such as... 

When an external magnetic field is applied to an initially stable suspension of magnetic particles, a dipolar interaction arises that leads to the formation of anisotropic aggregates aligned along the field direction. The final morphology of the structures mainly depends on the particle volume fraction of the colloidal suspension ... 

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