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

TL;DR

This paper investigates how entropy-driven order-by-disorder mechanisms influence the magnetic phases of a frustrated antiferromagnetic bilayer honeycomb lattice under magnetic fields, revealing multiple ordered states and phase transitions.

Contribution

It provides a detailed analysis of order-by-disorder effects in a classical Heisenberg model on a bilayer honeycomb lattice, highlighting new magnetic phases and symmetry breakings.

Findings

Identification of two distinct magnetization regions with different soft modes

Observation of a classical plateau at M=1/2 with broken Z2 symmetry

Crossover from paramagnetic to cooperative magnetic behavior at higher temperatures

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 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 $J_1=J_x=J_p/3$, 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 $Z_2$ 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, $J_1=J_x<J_p/3$.