The effects of laser irradiation on γ-Fe₂O₃ 4 ± 1 nm diameter maghemite nanocrystals synthesized by co-precipitation and dispersed into an amorphous silica matrix by sol-gel methods have been investigated as function of iron oxide mass fraction. The structural properties of γ-Fe₂O₃ phase were carefully examined by X-ray diffraction and transmission electron microscopy. It has been shown that γ-Fe₂O₃ nanocrystals are isolated from each other and uniformly dispersed in silica matrix. The phase stability of maghemite nanocrystals was examined in situ under laser irradiation by Raman spectroscopy and compared with that resulting from heat treatment by X-ray diffraction. It was concluded that ε-Fe₂O₃ is an intermediate phase between γ-Fe₂O₃ and α-Fe₂O₃ and a series of distinct Raman vibrational bands were identified with the ε-Fe₂O₃ phase. The structural transformation of γ-Fe₂O₃ into α-Fe₂O₃ occurs either directly or via ε-Fe₂O₃, depending on the rate of nanocrystal agglomeration, the concentration of iron oxide in the nanocomposite and the properties of silica matrix. A phase diagram is established as a function of laser power density and concentration.

A FePt-based hard-magnetic nanocomposite of exchange spring type was prepared by isothermal annealing of melt-spun ${\text{Fe}}_{52}{\text{Pt}}_{28}{\text{Nb}}_2{\text{B}}_{18}$ (atomic percent) ribbons. The relationship between microstructure and magnetic properties was investigated by qualitative and quantitative structural analysis based on the x-ray diffraction, transmission electron microscopy, and ${}^{57}\text{F}\text{e}$ Mössbauer spectrometry on one hand and the superconducting quantum interference device magnetometry on the other hand. The microstructure consists of $\text{L}{1}_0\text{-FePt}$ hard-magnetic grains (15–45 nm in diameter) dispersed in a soft magnetic medium composed by A1 FePt, ${\text{Fe}}_2\text{B}$ , and boron-rich (FeB)PtNb remainder phase. The ribbons annealed at $700°\text{C}$ for 1 h exhibit promising hard-magnetic properties at room temperature: ${\text{M}}_{\text{r}}/{\text{M}}_{\text{s}}=0.69$ ; ${\text{H}}_{\text{c}}=820\text{kA}/\text{m}$ and ${\left(\text{BH}\right)}_{\text{max}}=70\text{kJ}/{\text{m}}^3$ . Strong exchange coupling between hard and soft magnetic phases was demonstrated by a smooth demagnetizing curve and positive $\delta \text{M}$ -peak in the Henkel plot. The magnetic properties measured from 5 to 750 K reveals that the hard characteristics remains rather stable up to 550 K, indicating a good prospect for the use of these permanent magnets in a wide temperature range.