Direct evidence of chemical ordering in the FePt nanostructured alloy by HR-TEM

• Phase transformation in FePt were understood nano-scopically using high resolution-transmission electron microscopy.
• Fast Fourier Transform reveals structural ordering in FePt unit cell.
• An order parameter of 0.875 and coercivity 3 kOe respectively also supports the chemical ordering.

The iron–platinum (FePt) alloy exhibits structural and magnetic phase transformation even at a low temperature of 300 °C with an insignificant grain growth. These transformation studies were understood nano-scopically using high resolution-transmission electron microscopy (HR-TEM). The FePt grains show strain induced structural transformation and adopts polycrystalline behaviour. The chemical ordering of FePt grains is explained using Fast Fourier Transform (FFT) analysis of the TEM image. HR-TEM image shows the hexagonal arrangement of Pt atoms in the [0 0 1] direction in the FePt unit cell which gives the direct evidence of chemical ordering in FePt nanostructured alloy. The filtration and reconstruction method has been employed with the help of inverse Fast Fourier Transformation tool, confirming the formation of L10 FePt phase. The chemical ordering is also confirmed by structural and magnetic measurements revealing an order parameter of 0.875 and coercivity 3 kOe respectively at a low annealing temperature of 300 °C. The chemical ordering at low annealing temperature makes it suitable for media storage applications.