Structure and magnetic order in Fe2+xV1-xAl

We present a detailed structural investigation via neutron diffraction of d ifferently heat-treated samples of Fe(2)VAI and Fe2+xV1-xAl. The magnetic b ehaviour of these materials is also studied by means of mu SR and Mossbauer experiments. Our structural investigation indicates that quenched Fe2VAI, exhibiting the previously reported 'Kondo-insulating-like' behaviour, is of f-stoichiometric (6%) in its Al content. Slowly cooled Fe2VAl is structural ly better ordered and stoichiometric, and the microscopic magnetic probes e stablish long-range ferromagnetic order below T-C = 13 K, consistent with r esults from bulk experiments. The magnetic state can be modelled as being g enerated by diluted magnetic ions in a non-magnetic matrix. Quantitatively, the required number of magnetic ions is too large to be explained by a mod el of Fe/V site exchange. We discuss the implications of our findings for t he ground-stare properties of Fe2VAl, in particular with respect to the rol e of crystallographic disorder.