Magnetization experimental results with particles

The PEDM is able to explain the anomalous relaxation of solutions of ferritin and akaganeite particles, especially its linear dependence with Bq, the external magnetic field. The model is compatible with the observed dependence of the rate on pH. The relaxation rate predicted by the PEDM is proportional to the number of adsorption sites per particle (q) the values deduced for q from the adjustment of the model to experimental results (from NMR and magnetometry in solutions) are reasonable for hydrated iron oxide nanoparticles (63). 

Figure 14. Nilsson diagram for odd neutrons close to N = 82. The Fermi levels for N = 83, 85, and 87 indicate a successive filling of the/)/2 shell. On the right, the experimental magnetic dipole and electric quadrupole moments are compared with the results from particle-rotor calculations assuming deformations of e = 0.10 and 0.15. The trend of the quadrupole moments reproduces the increase of coupling to the collective motion, while the discrepancy in the trend for the magnetic moments is understood as a change of core polarization.

F.2.3.6. Comparison with Experimental Results. The experimental results for which the measurement parameters are controlled, which permits only the derivation of the various parameters included in the formulas and a checking of the models, were until now very limited. They concern Fe particles in Al Oj matrix and y-FCjOj particles We show an example in Figure F.2.8 for y-FCjOs particles. We can see from the figure that a weak curvature is observed for 1/x when H pp is parallel to the sample plane. It is also clear that the value of the intercept (the d p value) of the quasi-linear part of 1 ix with the temperature axis is strongly dependent of the thermal correction M ,(r)/M (0). That raises the problem of the determination of this variable. In fact, it is only directly measurable from neutron diffraction experiments (see Section F.8). It can be deduced from magnetization under high-field experiment (see Section F.3) on the condition that does not vary much with H pp. If this is not fulfilled, only approximate values are obtained, which leads to difficulties for a precise determination of the intercept. We shall discuss the A/ p(r)/A/ r(0) determination in Section F.3. 

The calculated remanent magnetization compares favorably with some experimental results reported on spin glasses/ described in terms of a clusters-fine particles model. However, as far as we know, the Khater model has not been applied to fine particles materials. Assumed distribution function is not realistic, as well as in most cases the absence of interparticle interactions. 

In this chapter, we have tried to carry out the restatement of the magnetic properties of fine particles resulting from the relaxation of their magnetic moments from theoretical as well as experimental points of view. We discussed the models, several with some details, that allow one to calculate the relaxation time of the particle magnetic moment, to evaluate the effect of the interparticle interactions, and to interpret the experimental results. We clearly stated our objections, without use of indirect sentences understandable only by specialists, because fine-particle studies can be of interest in various fields, for example, catalysis, biology, mineralogy. Of course, this is our opinion at the present time. 

This criterion is critical for convective assembly. It seems that it is less restrictive for capillary assembly. Recent studies have demonstrated that even in the case of sedimenting particles, it is still possible to perform capillary assembly, as long as particles are not interacting strongly with the template surface and can be dragged by the mean of capillary forces. Figure 15.16 shows experimental results obtained with 4.5 p.m magnetic particles (Dynal). 

The calculations were in agreement with the experimental results. Therefore, stable magnetic fluids with positively charged magnetite particles and with bilayer stabilized magnetite particles could be prepared. 

---