## 3 Results and Discussion
[30] explained the hysteresis of magnetic properties by the hysteresis of the consolidation of filler particles into elongated aggregates. Since it is expected that the hysteresis is determined by different microstructures in MAEs depending on the magnetization history, it can be expected that the hysteresis can be observed in the scattering curves. Figure 5 demonstrates the results of the scattering measurements. The following sequence of magnetic field strength was applied 0 T (denoted as (1) in Figure 5) \(\rightarrow\) 0.2 T (2) \(\rightarrow\) 0.35 T (3) \(\rightarrow\) 0.2 T (4) \(\rightarrow\) 0 T (5) \(\rightarrow\) 0.2 T (6) \(\rightarrow\) 0.35 T (7) \(\rightarrow\) 0.2 T (8) \(\rightarrow\) 0 T (9). Indeed, the hysteresis of scattering curves is observed also in our USANS experiments. In particular, it is clearly seen that the three curves (1, 5 and 9) obtained in the absence of a magnetic field are well separated from the family of curves obtained in the presence of a magnetic field. Moreover, these three curves do not coincide and they are progressively shifted towards the curves obtained in the presence of a magnetic field displaying the \"memory\" effect. Further, it is observed that the scattering curves 2 and 6 at 0.2 T corresponding to the ascending part of the hysteresis curve (i.e., when the field was increased from 0 to 0.2 T) are distinctly different from the scattering curves 4 and 8 at 0.2 T when the field was decreased from 0.35 T to 0.2 T and at 0.35 T. Interestingly, the scattering curves 4 and 8 seem to be similar to the curves 3 and 7 obtained in the maximum magnetic field. Figure 4: USANS curves of the MAE sample with 67 mass% of Fe and a stiff matrix for different magnetic fields. To qualitatively explain the observed differences in scattered curves, let us recall the known results on SANS scattering in a magnetic fluid [31]. The angle between the \(Q\)-vector and the magnetic field direction was set to be \(0^{\circ}\) (\(Q\)-vector parallel to the magnetic field direction), \(30^{\circ}\) and \(60^{\circ}\). In a magnetic fluid, the magnetic particles formed chain-like structures and a pronounced (Bragg) peak, corresponding to a resulting particle-particle distance was observed. The position of this peak was practically independent of the angle between the magnetic field vector and the \(Q\)-vector. From this one may conclude that for magnetic fluid, the inter-particle distance in chains determines the position of the scattering peak. In MAEs, the displacements of particles are limited by the matrix elasticity. For high concentrations of magnetizable particles in MAEs, numerical simulations showed that formation of chain-like structures may become impossible due to purely geometrical constraints [32]. Therefore, in MAEs it is more reasonable to speak about formation of elongated particle aggregates and not about chain formation. A physical picture of changes in internal MAE microstructure was proposed in [33]. Obviously, the arrangement of magnetic particle in an MAE becomes anisotropic. The corresponding physical properties, e.g., the (dielectric) permittivity become anisotropic as well [34]. We were able to observe the anisotropy of neutron scattering in MAE samples using a very-small-angle neutron scattering (VSANS) instrument, but there we could not avoid multiple scattering [35]. In our presented USANS experiments, the \(Q\)-vector is perpendicular to the magnetic field direction. We may speculate that typically structures larger than 25 \(\upmu\)m (elongated clusters) are formed in a highly filled sample (80 mass% of iron, see Figure 5). For such a highly loaded MAE, the existence of the three-dimensional magnetic-filler network already in the absence of a magnetic field can be expected. Intuitively, one would anticipate that the structures would elongate in field direction and, thus, this dimension would grow, while perpendicular structures would rather shrink by such alignment.