SCATTERING PROPERTIES OF THE TRIANGULAR ISING ANTIFERROMAGNET - DISORDER AND LIFSHITZ LINES

We study an anisotropic nearest-neighbor Ising antiferromagnet on the triangular lattice, using Monte-Carlo simulations and random-phase (or related) approximations. Our main interest concerns the high-temperat ure magnetic scattering. Exact results are available at the disorder l ine (Stephenson; Welberry and Galbraith). Of greater experimental sign ificance is the Lifshitz line where (i) splitting of the scattering pe aks occurs and (ii) dislocationlike defects appear in the (instantaneo us) spin configurations. A good analytical fit of the Lifshitz line is given by the Bethe-Peierls approximation. These results could be rele vant to other systems with disorder lines, e.g., the ANNNI model and m icroemulsions.