Abstract
FePt nanoclusters have been implanted onto polyimide films and subjected to thermal annealing in order to obtain a special magnetic phase (L10) dispersed within the polymer. SQUID measurements quantified the magnetic features of the as‐prepared and annealed hybrid films. As‐implanted FePt nanoparticles in polyimide films exhibited a blocking temperature of 70 ± 5 K. Thermal annealing in zero and 10 kOe applied magnetic field increased the magnetic anisotropy and coercivity of the samples. Wide Angle X‐Ray Scattering confirmed the presence of FePt and L10 phase. All samples (as deposited and annealed) exhibited electron spin resonance spectra consisting of two overlapping lines. The broad line was a ferromagnetic resonance originating from FePt nanoparticles. Its angular dependence indicated the magnetic anisotropy of FePt nanoparticles. SEM micrographs suggest a negligible coalescence of FePt nanoparticles, supporting that the enhancement of the magnetic properties is a consequence of the improvement of the L10 structure. The narrow ESR line was assigned to nonmagnetic (paramagnetic) impurities within the samples consistent with graphite‐like structures generated by the local degradation of the polymer during implantation and annealing. Raman spectroscopy confirmed the formation of graphitic structures in annealed KHN and in KHN‐FePt.
Highlights
Synthesis of magnetic clusters at submicron scale by gas aggregation is based on target atoms evaporating/sputtering into a cooled inert gas flow at relatively high pressure [1]
The photos show that the coalescence of the FePt nanoparticles is negligible and suggest that the FePt nanoparticles are eventually embedded within a layer which resulted from the local modification of the polymeric matrix
For FePt nanoparticles obtained by chemical reductions the lines assigned to (001) and (110) reflections have been reported as absent [4], while in the case of FePt nanoclusters these lines are well resolved
Summary
Synthesis of magnetic (metal) clusters at submicron scale by gas aggregation is based on target atoms evaporating/sputtering into a cooled inert gas flow at relatively high pressure [1]. Collisions cascade between metallic atoms and carrier gas results in the nucleation of supersaturated metal vapors into clusters. This method produces high purity clusters with diameters below 10 nm and deposition rates of the order of 1 A /s [1, 2]. The L10 phase has an “ordered” slightly distorted fcc structure ( is a face centered tetrahedral lattice), as beyond the lattice ordered structure, the base atoms (Fe and Pt) are orderly distributed ( one atom occupies two opposite faces of the crystalline lattice and the other atoms occupy the remaining sites) [3]. The degree of “atom base order” in FePt is quantified by the ordering parameter S [5]: S
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