MAGNETIC ENTROPY CHANGE IN A TWO-DIMENSIONAL ANTIFERROMAGNETIC SQUARE LATTICE

Abstract

In this study, we investigate magnetic entropy variation and magnetocaloric properties as a function of frustration by considering a spin-1/2 antiferromagnetic Heisenberg model on a square lattice with nearest (J1) and next-nearest neighbor exchange interaction (J2). We show that the degree of frustration in the square lattice increases with α=J2/J1. While the square lattice is unfrustrated for α = 0, it becomes fully frustrated for α=0.5. Numerical results show that the entropy of the square lattice approaches zero for the unfrustrated case at T=1 K. In contrast, finite entropy can survive in the frustrated case at the same temperature. We also calculate the magnetic entropy change (ΔSm) in the square lattice and show that the maximum value of ΔSm increases with increasing α. These results indicate that the magnetic entropy change and consequently the magnetocaloric effect can be enhanced by increasing the degree of frustration. We conclude that the enhanced magnetocaloric effect is related to quantum fluctuations and disordered ground state present in the frustrated square lattice.