Thermal annealing effects on the structural, magnetic and hyperfine properties of the Fe/SnO2/Fe thin film deposited by RF sputtering method

Abstract

In the present work, the effect of the post-deposition annealing process in an air atmosphere on the structural and magnetic properties of the ternary Fe/SnO2/Fe thin film, deposited by the sputtering technique was reported. X-ray diffraction (XRD) pattern confirms the formation of alpha-iron, magnetite and fin dioxide phases in the as-deposited film. Meanwhile, after the thermal annealing, the formation of hematite and fin dioxide phases was determined. Magnetization (M) measurements reveal some features after the annealing: i) a reduction of the coercive field (H-c), which has been assigned to the presence of hematite, and ii) the transformation of alphairon/magnetite phases into the hematite phase in accordance with results obtained from XRD data analysis. Those results were also confirmed by room temperature Conversion electron Mossbauer spectroscopy (CEMS) measurements carried out using a Co-57(Rh) source. Furthermore, the doublets of the CEMS spectrum of the asdeposited film (21%) has been assigned to the signal of Fe3+ and Fe2.5+ (mixture of Fe3+ and Fe (2+)) ions, which diffuse into the SnO2 matrix. The spectral area of those doublets is clearly reduced to 3% after the thermal annealing. It suggests the migration of the Fe ions from the non-magnetic phase to the magnetic phase. On the other hand, CEMS spectrum of the as-deposited film carried out with using a Sn-119m source is well modeled with a doublet and a sextet. The doublet was assigned to Sn4+ ions of the SnO2 phase; meanwhile, the sextet was assigned to Sn4+ ions located at interstitial and/or substitutional sites of the alpha-iron/magnetite phases. Those fin ions sense the supertransferred hyperfine field from Fe neighbor. After the thermal annealing, the CEMS spectrum was well modeled with only a doublet related to SnO2 phase, suggesting that the fin ions have been out diffused from the magnetic phase (alpha-iron and magnetite) and incorporate into the no magnetic o-SnO2.