Field-induced multiple order-by-disorder state selection in an antiferromagnetic honeycomb bilayer lattice

Abstract

In this paper we present a detailed study of the antiferromagnetic classical Heisenberg model on a bilayer honeycomb lattice in a highly frustrated regime in the presence of a magnetic field. This study shows strong evidence of entropic order-by-disorder selection in different sectors of the magnetization curve. For antiferromagnetic couplings J1=Jx=Jp/3, we find that at low temperatures there are two different regions in the magnetization curve selected by this mechanism with different number of soft and zero modes. These regions present broken Z2 symmetry and are separated by a not fully collinear classical plateau at M=1/2. At higher temperatures, there is a crossover from the conventional paramagnet to a cooperative magnet. Finally, we also discuss the low-temperature behavior of the system for a less frustrated region, J1=Jx.