Evidence of classical order-by-disorder in highly frustrated bilayer honeycomb lattice

F. A. GÓMEZ ALBARRACÍN; H. D. ROSALES; M. E. ZHITOMIRSKY

Trieste

Conferencia; Conference on Frustration, Disorder and Localization: Statics and Dynamics; 2015

Frustration has proved to give rise to an extremely rich phenomenology in both quantum and classical systems. The inclusion of an external magnetic field could change the degeneracy and topology of the ground state manifold stabilizing different ground states. Experimentally, in the last few years evidence of frustration has been found inBi3Mn4O12(NO3). This material has been established as a quasi-two dimensional lattice with spin-3/2 where the Mn4+ ions are arranged in a bilayer antiferromagnetic honeycomb lattice. Because of the large value of the Curie-Weiss temperature and the lack of long range order at low temperatures, antiferromagnetic interactions and the presence of strong frustration are to be expected. First principles calculations suggest the existence of weak intralayer frustrating coupling but strong interlayer coupling and possible frustration between layers. Motivated by this, in this work we present a thorough study of a classical bilayer honeycomb lattice with frustrating interlayer couplings. We show that in some particular cases this system is highly frustrated and has a degenerate ground state. We study through Monte Carlo simulations its behaviour with temperature under an external magnetic field. We find that, depending on thisfield, different states are selected from the ground state manifold through the order by disorder mechanism. We study different parameters to define the selected states, broken symmetries andphase transitions, and present the h-T phase diagram. Using analytical calculations and the specific heat curve simulations, we show that there are soft and zero modes in the thermal fluctuations of different states, which give rise to their selection due to order by disorder.