LOCAL MAGNETIC-MOMENT AND HYPERFINE FIELD IN HYDROGENATED IRON AND IRON-VANADIUM ALLOY

The local magnetic moment mu and hyperfine field B-hf at Fe and V site s in hydrogenated iron and iron-vanadium were calculated using the dis crete variational method. The variations in mu and B-hf with H occupat ion of the octahedral (O) site were considered. It was found that when H occupies the O site neighbouring an Fe atom, both local moment and hyperfine field at this atom decrease linearly with increasing number of Il atoms. The rate of decrease is larger for Fe in iran as compared to iron in vanadium. On the other hand, when H resides at an O site n ext neighbouring an Fe atom, whether in iron metal or in iron-vanadium , the Fe magnetic moment increases slowly, while the hyperfine field r emains almost constant. The V moment in iron, which is negative (simil ar to -0.83 mu B), becomes less negative (similar to -0.30 mu B) as H occupies the neighboring O sites, whereas slight changes occur(similar to -0.88 mu(B)) when H is at the next neighbouring O site. The net ef fect of H on Fe in iron is to decrease the average magnetic moment at a rate of similar to 1.2 mu(B) per H/Fe for low H content. On the othe r hand, the average Fe moment in an iron-vanadium alloy increases if H resides at O sites which are immediate neigbours of V and next neighb ours of Fe. This may explain the development of a magnetic state on hy drogenation of Fe-V alloys, which is exhibited by the specific heat an d susceptibility measurements. The changes in the isomer shift were fo und to agree with experimental trends.