CALCULATIONS OF THE SOFT MODE OF MAGNONS ON A (001) SURFACE FOR A SEMIINFINITE CUBIC FRUSTRATED ANTIFERROMAGNET

We have carried out a theoretical study of the (001) surface magnon di spersion curves. Their localized energy states are calculated by the G reen function and matching procedure methods which are used simultaneo usly in the case of semi-infinite cubic frustrated Heisenberg antiferr omagnets. Magnetic frustration phenomena originate from competing effe cts between first neighbour (J(AB)(1 nu)) and second neighbour (J(AA(B B))(2 nu) interactions. This magnetic frustation is quantized by the J (AB)(1 nu)/J(AA(BB))(2 nu) approximate to 4, a magnetic phase transiti on also exists at the surface, as previously observed in the bulk, in accordance with the results predicted by computer simulation.