Magnetoelastic instability in Ising-like models

Abstract

The magnetoelastic instability in nanostructured ring-shaped Ising-like spin 1/2 model has been investigated by using the exact diagonalization method. It is found that there exists two critical anisotropy parameters Δ c ( 1 ) and Δ c ( 2 ) ( Δ c ( 1 ) < Δ c ( 2 ) ) in the phase diagram. As the anisotropy parameter Δ > Δ c ( 2 ) , the magnetoelastic transition from dimerized phase to uniform phase is a first order transition with an increase of the lattice spring constant. While for Δ < Δ c ( 2 ) , the transition is continuous. Another critical value Δ c ( 1 ) divides the different lattice distortion behavior as the anisotropy is strengthened.