Magnetization Process in Two-Dimensional Coupled Plaquette System on the 1/5-Depleted Square Lattice

Abstract

Magnetization process in the S =1/2 Heisenberg antiferromagnet with plaquette structure and up to second neighbor couplings on the 1/5-depleted square lattice is studied by using perturbation expansion and exact diagonalization methods. This model describes the magnetism of CaV 4 O 9 for an adequate choice of the exchange parameters. Within first order calculations it is shown that plateaus at m =1/8, 1/4 and 3/8 appear for some parameter region of the exchange interactions, where m denotes magnetization per a spin. The magnetization curve for CaV 4 O 9 is calculated, which shows that the 1/4-plateau is clearly observed and CaV 4 O 9 is almost right at the quantum critical point of the 3/8-plateau. Critical behavior of the 1/4-plateau is also discussed.