Theoretical Analysis of the "Double-q" Magnetic Structure of CeAl2

الأصل · EN

A model involving competing short-range isotropic Heisenberg interactions is developed to explain the "double-q" magnetic structure of CeAl₂. For suitably chosen interactions, terms in the Landau expansion quadratic in the order parameters explain the condensation of incommensurate order at wavevectors in the star of (1/2 -δ, 1/2 +δ, 1/2)(2π/a), where a is the cubic lattice constant. We show that the fourth order terms in the Landau expansion lead to the formation of the so-called "double-q" magnetic structure in which long-range order develops simultaneously at two symmetry-related wavevectors, in striking agreement with the magnetic structure determinations. Based on the value of the ordering temperature and of the Curie-Weiss Θ of the susceptibility, we estimate that the nearest neighbor interaction K₀ is ferromagnetic, with K₀/k=-11± 1K and the next-nearest neighbor interaction J is antiferromagnetic with J/k=6 ± 1K. We also briefly comment on the analogous phenomenon seen in the similar system TmS.