Hyperfine and Structural Properties of the Mechanically Alloyed (FeMn)30Cu70 System

Nanostructured Fe15Mn15Cu70 alloys were prepared by high-energy ball milling. The alloying process spans grinding times from 15 minutes to 114 hours. The Moessbauer isomer shifts are analyzed at 77 K and 4.2 K as a function of the average lattice parameter determined from Rietveld analysis of the X-ray diffraction data. Evidence of two different iron sites at 77 K to account for the asymmetry of the Moessbauer spectra is discussed by correlating hyperfine and structural parameters. This leads to conclude the occurrence of a low-spin to high-spin partial transition of iron at a critical volume of around 50 A3 at 77 K, supporting theoretical predictions.