Amorphous yttrium-iron alloys. II. Mossbauer spectra

For pt.I see ibid., vol.11, no.12, p.2727 (1981). Mossbauer data are presented for eight Y 1-x Fe x alloys with 0.32<or=x<or=0.88 in the temperature range 1.5-300K. In some cases external magnetic fields of up to 140 kOe were applied. Iron in the x=0.32 sample has essentially no magnetic moment. Magnetism in zero field appears near x=0.4 and the fraction of non-magnetic iron corresponds to the fraction possessing seven or more yttrium neighbours. The iron moment increases with the number of iron neighbours beyond six. An ordered state with a random non-collinear structure is found for all compositions except x=0.32. Data in an applied field of 50 kOe are interpreted in terms of idealised asperomagnetic structures where the iron moments are oriented at random within a cone of half-angle psi . psi decreases with increasing x, but collinear saturation cannot be achieved in any laboratory field. The average hyperfine field of iron in Y 0.29 Fe 0.71 varies as (H hf (T))=(H hf (0))-cT n below 40K where n=1.1+or-0.1. An explanation is suggested in terms of single atom excitations where iron atoms in environments barely suitable for the existence of a moment are excited to low-lying non-magnetic states.