Highly Controlled Dip-Coating Deposition of <i>fct</i> FePt Nanoparticles from Layered Salt Precursor into Nanostructured Thin Films: An Easy Way To Tune Magnetic and Optical Properties

Nanostructured titania films containing hard magnetic FePt nanoparticles were obtained through impregnation and postannealing of salt layered precursor [Fe­(H₂O)₆]­[PtCl₆] nanocrystals. The impregnation was performed by a highly controlled dip-coating process into ethanol based solutions of the salt precursor. The bimetallic salt nanocrystals were formed upon evaporation of the solvent into the cavities of TiO₂ template films. The salt was transformed into the hard magnetic <i>fct</i> phase by annealing in reductive atmosphere at 400 °C a particularly low conversion temperature compared with those reported for other synthesis approaches. Two different titania templates were considered. In the first case, the impregnation of 3D mesoporous films was investigated in order to determine the influence of the deposition parameters on the amount of FePt nanoparticles embedded and the final optical and magnetic properties of the layers. In the second case, this approach was further extended to 2D heterogeneous nanoperforated films. The nanoparticles were selectively deposited into the perforations thanks to a prior functionalization of the titania template by the formation of hydrophobic/hydrophilic distinct domains. Interestingly, the coalescence between the magnetic particles was found to be limited due to the low conversion temperature. This procedure of positioning particles onto a 2D nanostructured support constitutes an easy and versatile bottom-up approach toward magnetic arrays with potential application in magnetic data storage devices