# Magnetic Behaviour of Iron Oxide/Dextran Nanoparticles in a Keratin Matrix
## 3 Results
Combined with the AFM data, this might indicate that the MNPs are present in clusters of various dimensions. In addition, they are either completely missing in the flat regions or they are scattered and isolated with a density below the detection limit of EDX. Figure 6 presents some NanoMOKE maps obtained for the same sample as in Figure 5 and recorded at 300 and 15 K. In (a) and (c), the reflectivity maps are reported, i.e., the local reflection of the laser beam. Keratin is largely transparent, and the laser can therefore penetrate the whole film and access the MNPs dispersed throughout the whole thickness of the film [20]. In (b) and (d), the maximum Kerr rotation values at 2000 Oe are plotted using a color scale. It is possible to notice that the more reflective areas do not show any noticeable magnetic contrast. However, in these areas, the average Kerr signal increases at 15 K. At 300 K, the dark regions that can be identified with clusters present some magnetic contrast with stronger Kerr rotation values that also increase at 15 K. The spatial distribution of the Kerr signal provides a complex picture, i.e., it appears that not all MNPs in a cluster align perpendicular to the surface as the setup works in a polar configuration. NanoMOKE can thus provide a fine map of the local magnetization. Figure 4: AFM morphologies of all the samples analyzed. The % concentration value is indicated for each image. Figure 5: Environmental SEM of a 20% sample: (**a**) topographic image; (**b**) EDX chemical analysis of the cluster indicated with a red square in (**a**) showing Fe and O peaks. These peaks are not detected in the flat areas (orange point in (**a**) and orange line in (**b**)). Figure 6: NanoMOKE maps of a 20% sample at 300 and 15 K. In (**a**,**c**), the reflectivity maps are reported, i.e., the local reflection of the laser beam. In (**b**,**d**), the maximum Kerr rotation values at 2000 Oe are plotted. The clusters show a stronger magnetic response that increases at low T. The surrounding areas present a weaker signal that is, however, higher at low T.  
Figure 7 presents some NanoMOKE maps obtained for a pure keratin sample: the maximum Kerr rotation values at 2000 Oe are plotted using a color scale. These maps are homogeneous, both in reflectivity and Kerr rotation values. The average Kerr signal is slightly negative at 300 K, though the difference in relation to 15 K is very small. More interestingly, it is always lower than the average Kerr signal obtained from the bright regions of the 20% sample at both room and low T. This observation may indicate that the bright regions, made prevalently of keratin, may have the presence of some isolated MNPs. These MNPs must be dispersed as single ones or form small clusters, all of them well diluted and in depth, as neither AFM nor ESEM can detect their presence. In Figure 8, some NanoMOKE data are presented for the same 20% sample. Specifically, some graphs are shown of Kerr rotation versus H obtained at 300 and 15 K. The Kerr rotation value is proportional to the local magnetization. The curves were recorded at three spots in Figure 6: one within a cluster and two within the bright areas. Pure keratin data are also reported as a reference. As expected, the data of pure keratin do not depend on T. At 300 K, the curves recorded in the cluster have a stronger signal compared to the curves recorded in the bright region. One spot of the bright regions is similar to pure keratin, whereas the other one shows signals slightly stronger than those obtained on pure keratin. At 15 K, the signal increases in the cluster region and also in the bright regions, though to a lesser extent. This is an indication of the presence of MNPs not only in the clusters, as  
Figure 7: NanoMOKE maps of a pure keratin sample at 300 and 15 K. In (**a**,**c**), the reflectivity maps are reported, i.e., the local reflection of the laser beam. In (**b**,**d**), the maximum Kerr rotation values at 2000 Oe are plotted.