Fe57 hyperfine field distributions in Fe - 28 per cent Ni - 3 per cent C invar alloy

The hyperfine field distribution has been measured for Fe - 28 per cent Ni - 3 per cent C alloy at 22 K with a longitudinal external field. Relative Mössbauer line intensities indicate that the effective hyperfine field at Fe⁵⁷ nuclei lower than 30–40 kOe tends to align perpendicular with a 50 kOe external field which is explicable only by the model of coexistence of antiferromagnetic and ferromagnetic Fe states.