Magnetic properties of a graphene-like Heisenberg system with four-sublattice superlattice

Abstract

The magnetic properties of a graphene-like Heisenberg system with four-sublattice superlattice are studied using the linear spin-wave theory. The spin-wave spectra have four branches with two energy gaps. The effects of intralayer exchange coupling and anisotropy on the energy gap width are analyzed, especially when the spin of sublattice A varies. These results help optimizing energy gaps and spin-wave resonance frequencies. At low temperature, magnetic moments remain nearly constant before decreasing with increasing temperature. At ground state, quantum fluctuations reduce sublattice magnetic moments below classical values. Sublattices C and D show a crossing point at their magnetic moments due to quantum, thermal fluctuations and spin frustration.