**Author details**

The sample Sr005, even if thermally treated under laser light, remains stable showing the same Raman spectrum during the whole laser-induced thermal cycle. Small peak shifts are due to temperature effects on lattice parameters. On the contrary for Al01 sample, it is evident that upon irradiation, the Raman spectrum of the Al01 change markedly and the typical Raman features of hematite appear when the sample is maintained under laser light having

thermal cycle, the signal of hematite is still observable indicating a stable conversion. This is an indirect proof that at the beginning of the thermal cycle nanoregions in the irradiated volume had a structure different from the proper ZFO structure. It is likely that nanoregions of maghemite or highly defective Zn deficient zinc ferrite layers were present. We underline

Only three samples exhibit a stable pure zinc ferrite phase with no hematite detected at the end of the thermal cycle: ZnFe-SS, Ca025, and Sr005. The first exhibited a paramagnetic behavior, while the latter were found to be superparamagnetic. The phase stability proved by monitoring the Raman spectrum under laser heating is fundamental to validate the quality of the powders with good magnetic functional parameters, in particular in view of applications

This chapter gave a look on the potential of Raman spectroscopy when applied to nanosized

functional properties, and it is used in magnetic storage, ferrofluids, catalysis, and biomedical applications, as for instance theranostics and hyperthermia. For the latter applications, a strong requirement is the superparamagnetic behavior at RT, which take place in zinc ferrites thanks to the nanometric scaling. This behavior has been revealed even in pure ZFO nanoparticles due to the inversion between divalent and trivalent cations on the tetrahedral and octahedral sites of the spinel-type structure. In this frame, thanks to its intrinsic sensitivity to chemical and structural composition, Raman spectroscopy has been widely used to monitor cations distribution in pure and doped zinc ferrites. In the first part of the chapter, the state of the art concerning the results from Raman scattering in pure and doped zinc ferrites has been presented in connection to the different synthesis methods employed to obtain high quality nanostructured ferrites. It appears clear how detailed analyses on Raman data allow to evaluate the influence of nanometric scaling on Raman lines features—peak energies, widths and shape, to obtain information on the inversion degree, to reveal the presence of extrinsic iron oxides phases like hematite or magnetite and to monitor stability of spinel ferrites vs. light exposure or thermal treatment. This information is essential to assess the functional quality of the materials and it is essential to study and understand the close correlation between functional parameters and morphology, gran size, intentional doping, cation distribution, and nanoparticle architecture. Indeed magnetic, structural and chemical purity and homogeneity of nanoparticles must be thoroughly verified because even low amount of extrinsic phases can alter the functional properties. Indeed, low amount of hematite or maghemite can alter the long-term stability of nanoparticles especially in biological environment, favoring aggregation.

O4

. When the laser light is attenuated at the end of the

display a peculiar mixing of high-quality

a power density equal to 2 × 10<sup>5</sup> W/cm<sup>2</sup>

in biomedical field.

244 Raman Spectroscopy

**3. Conclusions and outlook**

zinc ferrites. The nanostructured spinel ZnFe<sup>2</sup>

that the grain sizes for Al01 and Sr005 are similar.

Pietro Galinetto<sup>1</sup> \*, Benedetta Albini<sup>1</sup> , Marcella Bini<sup>2</sup> and Maria Cristina Mozzati<sup>1</sup>

\*Address all correspondence to: pietro.galinetto@unipv.it

1 Department of Physics and CNISM, University of Pavia, Pavia, Italy

2 Department of Chemistry, University of Pavia, Pavia, Italy
