α-Fe nanopowder synthesised in low-pressure microwave plasma and studied by Mössbauer spectroscopy

An iron-based nanocomposite has been prepared by the microwave plasma method: Fe(CO)₅ vapour was introduced into an argon discharge at ∼1 kPa. The synthesised nanopowder was passivated in situ with a mixture of Ar and air. The as-prepared nanopowder was characterised by XRD, TEM, Raman and Mössbauer spectroscopies. In the XRD pattern of the nanopowder the α-Fe (d_XRD = 14 nm, 76 wt.%) and Fe₃O₄ (d_XRD = 3 nm, 24 wt.%) phases were identified only. α-Fe cores covered with oxide shells were observed under TEM. A huge increase of Mössbauer absorption was observed after the sample was cooled down to 5 K. The results of magnetic and thermal properties studies at low and high temperature are presented. The heat capacity of the sample exhibited an unexpectedly high value of 599 J/kg/K.