Magnetic Analysis of MgFe Hydrotalcites as Powder and Dispersed in Thin Films within a Keratin Matrix

Abstract

Hydrotalcites (HTlcs) are a class of nanostructured layered materials that may be employed in a variety of applications, from green to bio technologies. In this paper, we report an investigation on HTlcs made of Mg and Fe, recently employed to improve the growth in vitro of osteoblasts within a keratin sponge. We carried out an analysis of powder materials and of HTlcs dispersed in keratin and spin-coated on a Si/SiO₂ substrate at different temperatures. A magnetic study of the powders was carried out with a Quantum Design Physical Property Measurement System equipped with a Vibrating Sample Magnetometer. The data gathered prove that these HTlcs are fully paramagnetic, and keratin showed a very small magnetic response. Optical and Atomic Force Microscopy analyses of the thin films provide a detailed picture of clusters randomly dispersed in the films with various dimensions. The magnetic properties of these films were characterized using the Nano Magneto Optical Kerr Effect (NanoMOKE) down to 7.5 K. The data collected show that the local magnetic properties can be mapped with a micrometric resolution distinguishing HTlc regions from keratin ones. This approach opens new perspectives in the characterization of these composite materials.

Keywords: Keratin; NanoMOKE; PPMS-VSM; hydrotalcites; magnetic properties; thin films.

Figure 1

(a) Sketch of the structure of MgFe HTlc; (b) 3D representation of the keratin molecule.

Figure 2

X-ray diffraction pattern of the HTLc powder.

Figure 3

Magnetization (M) versus Temperature (T) plot of PPMS-VSM data obtained on HTlc powder, applying a static field of 100 mT, from T = 2.5 to 300 K.

Figure 4

Magnetization (M) versus Field (B) plots of PPMS-VSM data obtained on HTlc powder, applying a static field from −9000 to 9000 mT, at T = 10 and 300 K.

Figure 5

AFM images showing the morphology of (a,b) a keratin film and (c,d) a 2.5% 220 nm sample.

Figure 6

(a) SEM image of a 2.5% 220 nm sample. (b) EDX spectrum carried out in the area defined by the black dotted rectangle.

Figure 7

A comparison between (a) an optical image and (b) a NanoMOKE reflection map of the same area on a 2.5% 220 nm sample.

Figure 8

NanoMOKE data recorded scanning along a single line (in green) at 300 K. (a) Reflectivity map. Profiles of (b) reflectivity and (c) maximum Kerr rotation versus position of a keratin film (red line) and a 2.5% 220 nm sample (black line).

Figure 9

NanoMOKE data recorded scanning along a single line (in green) at 7.5 K. (a) Reflectivity map. Profiles of (b) reflectivity and (c) maximum Kerr rotation versus position of a keratin film (red line) and a 2.5% 220 nm sample (black line).

Figure 10

Kerr rotation versus B plots of three regions at 300 K: a pure keratin film, keratin only in a 2.5% 220 nm sample, and clusters in a 2.5% 220 nm sample.

Figure 11

Kerr rotation versus B plots of three regions at 7.5 K: a pure keratin film, keratin only in a 2.5% 220 nm sample, and clusters in a 2.5% 220 nm sample.

Figure 12

NanoMOKE data recorded on a square region of a 2.5% 220 nm sample at 7.5 and 300 K; see Figure 7. (a,b) Reflectivity maps. (c,d) Maps in false colors of the maximum Kerr rotation at B = 200 mT.