Exchange interactions in hydrogen-induced amorphous YFe2

The magnetic properties of hydrogen-induced amorphous (HIA) YFe2Hx (x = 1.8, 3.0 and 3.4) alloys have been investigated by means of 57Fe Mössbauer spectroscopy and atomic pair distribution analysis. The exchange integral (J) estimated from the temperature dependence of the average 57Fe hyperfine field shows a tendency to decrease with decreasing the average Fe–Fe interatomic separation. Moreover, an abrupt drop of J is evident at an average Fe–Fe interatomic separation of about 0.25 nm, which is the empirical threshold where the magnetic interaction between Fe moments changes from ferromagnetic to antiferromagnetic. The absence of a spin-glass state in HIA YFe2(H) is well understood by the enhancement of J through the volume expansion induced by the absorption of hydrogen.