Structural and magnetic properties of co-sputtered Fe0.8C0.2 thin films
PHYSICAL REVIEW MATERIALS
We studied the structural and magnetic properties of Fe 0.8 C 0.2 thin films deposited by co-sputtering of Fe and C targets in a direct current magnetron sputtering (dcMS) process at a substrate temperature (T s ) of 300, 523, and 773 K. The structure and morphology were measured using x-ray diffraction (XRD), x-ray absorption nearedge spectroscopy (XANES) at Fe L and C K edges and atomic/magnetic force microscopy (AFM, MFM). An ultrathin (3-nm) 57 Fe 0.8C0.2 layer, placed between relatively
... tween relatively thick Fe 0.8 C 0.2 layers was used to estimate Fe selfdiffusion taking place during growth at different T s using depth profiling measurements. Such 57 Fe 0.8C0.2 layer was also used for 57 Fe conversion electron Mössbauer spectroscopy (CEMS) and nuclear resonance scattering (NRS) measurements, yielding the magnetic structure of this ultrathin layer. We found from XRD measurements that the structure formed at low T s (300 K) is analogous to Fe-based amorphous alloy and at high T s (773 K), predominantly a Fe 3 C phase has been formed. Interestingly, at an intermediate T s (523 K), a clear presence of Fe 4 C (along with Fe 3 C and Fe) can be seen from the NRS spectra. The microstructure obtained from AFM images was found to be in agreement with XRD results. MFM results also agree well with NRS as the presence of multi-magnetic components can be clearly seen in the sample grown at T s = 523 K. The information about the hybridization between Fe and C, obtained from Fe L-and C K-edge XANES also supports the results obtained from other measurements. In essence, from this work, a possibility for experimental realization of Fe 4 C has been demonstrated. It can be anticipated that by further fine-tuning of the deposition conditions, even single-phase Fe 4 C can be realized which hitherto remains an experimental challenge.