Fabrication of FePt/M (M=C, Ag) Nanoparticulate Thin Films with Perpendicular Anisotropy

Abstract

ABSTRACTMagnetic nanoparticles with perpendicular anisotropy are attractive for applications in high-density recording media. For these applications, it is highly desirable to have particles with a size below 8 nm, a uniform size distribution, and a reduced ordering temperature to avoid unwanted particle agglomeration upon the required heat treatment to obtain the high anisotropy ordered L10 structure. In this work, FePt nanoparticles embedded in non-magnetic matrices M (M=C, Ag) have been fabricated by sputtering FePt and M multilayered thin films onto single crystal MgO [100] substrates at elevated temperatures up to 650 °C. The transformation from the disordered fcc to the ordered L10 phase in FePt nanoparticles was observed at temperatures as low as 300 °C. Besides the reduced transformation temperature, the deposited material showed an improved [001] texture for FePt/Ag thin films as compared to FePt/C due to lattice parameter matching between Ag and FePt. As the deposition temperature increases, the degree of atomic ordering approaches that of the fully ordered phase as indicated by the shift in the [002] XRD peak. TEM images showed that isolated particles with smaller average particle size (around 7 nm) were formed when the thickness of sputtered film is less than 4 nm. However, with a further increase of thickness of sputtered FePt film, a continuous layer of FePt particles was observed and the coercivity decreased rapidly due to a domain wall motion mechanism.