Frustrated magnetic interactions in an S=3/2 bilayer honeycomb lattice compound Bi3Mn4O12<

Abstract

Inelastic neutron scattering study has been performed in an S=3/2 bilayer honeycomb lattice compound Bi3Mn4O12(NO3) at ambient and high magnetic fields. Relatively broad and monotonically dispersive magnetic excitations were observed at ambient field, where no long range magnetic order exists. In the magnetic field-induced long-range ordered state at 10 T, the magnetic dispersions become slightly more intense, albeit still broad as in the disordered state, and two excitation gaps, probably originating from an easy-plane magnetic anisotropy and intrabilayer interactions, develop. Analyzing the magnetic dispersions using the linear spin-wave theory, we estimated the intraplane and intrabilayer magnetic interactions, which are almost consistent with those determined by ab initio density functional theory calculations [M. Alaei et al., Phys. Rev. B 96, 140404(R) (2017)], except the 3rd and 4th neighbor intrabilayer interactions. Most importantly, as predicted by the theory, there is no significant frustration in the honeycomb plane but frustrating intrabilayer interactions probably give rise to the disordered ground state.

An effective field theory approach for the $S = 3/2$ bilayer honeycomb antiferromagnet

“…In this work we have studied the Heisenberg model on the bilayer honeycomb lattice with in-plane first neighbor (J 1 ) and inter-layer first-(J 0 ) and second-neighbor (J x ) interactions, using a path integral approach. For values of the magnetic couplings close to those obtained experimentally 36 in Bi 3 Mn 4 O 12 (NO 3 ), where the dominant coupling is J 1 , the classical model presents a zero mode parametrized by the relative angle between the spins of each plane. The low energy effective theory of quantum fluctuations can be written in terms of a symmetric field, related to global magnetization, and an antisymmetric field related to the spin imbalance between layers.…”

“…If J 1 is the dominant coupling (as expected for Bi 3 Mn 4 O 12 (NO 3 )) 36 , increasing J x we find that m 3 = 0 at J x = J 0 /3 (see (12)), whereas µ j > 0, j = 1, ..., 4.…”

“…Nonetheless, the presence of a anisotropy term H D = r,l,η D(S z l,η ) 2 , with D > 0, would provide a finite contribution to all four µ j , j = 1, ..., 4, stabilizing the magnetization fluctuations. This scenario is beyond the scope of our present work because the point J 1 = J x = J 0 /3 is far away from the experimental and numerical estimations of the magnetic interactions in Bi 3 Mn 4 O 12 (NO 3 ), where J 1 is the dominant coupling 36 . Besides, our classical ground state corresponds to the limit of low frustration whereas for J 1 = J x = J 0 /3 frustration is dominant and leads to more general classical ground states.…”

“…The spins are coupled through Heisenberg isotropic interactions J 1 , J x and J 0 . For Bi 3 Mn 4 O 12 (NO 3 ), experimental and numeric results 36 show that J 1 is the dominant coupling, and J 0 is roughly three times the value of the J x . To connect with previous results in this system, let us write the Hamiltonian as a sum of terms over the square plaquettes schematized in figure (1-c).…”

Van Hove singularity in the magnon spectrum of the antiferromagnetic quantum honeycomb lattice

“…In the opposite limit of isotropic spin interactions, frustrated quantum magnetism can arise through the competition of nearest neighbor and nextnearest neighbor interactions [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] . Indeed, most honeycomb lattice materials studied thus far require the addition of further neighbor interactions to explain the underlying physical behavior 6,8,[38][39][40][41][42][43][44][45][46][47] . Such materials, with a complicated phase diagram as a function of first, second, and third nearest-neighbor interactions, have been fertile ground for exploration.…”