Pulsed laser deposited Co2FeSi Heusler alloy thin films: Effect of different thermal growth processes

Heusler alloy of Co2FeSi (CFS) is a promising candidate for spintronics applications due to its high magnetic moment and high spin polarization. In this report two series of CFS thin films of approximate thickness of 1000 Å were prepared using Pulsed Laser Deposition (PLD) technique by two separate routes, viz., (i) by depositing at elevated substrate temperature and (ii) by depositing at room temperature followed by post-deposition annealing under vacuum. The effects of these two thermal growth processes on the structural and magnetic properties of the films have been studied in detail here. X-ray diffraction study suggests that similar to the bulk target cubic Heusler phase is maintained in the thin films prepared by both the processes, however, X-ray reflectivity study shows that the films deposited at elevated substrate temperatures have higher density and surface roughness than the other set. Co/Fe atomic ratio in the films was found to remain near stoichiometry up to high temperature in both the series of samples though atomic percentage of Si is found to be higher in the samples. Synchrotron based Extended X-ray absorption fine structure (EXAFS) measurements indicate higher 3d-3p (Co-Si) hybridization for the series of samples prepared at elevated temperature while stronger 3d-3d (Co-Fe) hybridization for the samples prepared with post deposition annealing. EXAFS study also indicated presence of Co/Fe type antisite disorder which increases with increase in the substrate temperature. Finally from detail magnetic measurements it was observed that the films prepared by post-deposition annealing process have lesser crystallinity, magnetic ordering and magneto crystalline anisotropy in comparison to the films grown with elevated substrate heating.