Manifestations of bound-magnon crystal, uniform and cluster-based Haldane states in a spin-1 Heisenberg diamond chain().

Magnetic and thermodynamic properties of the antiferromagnetic spin-1 Heisenberg diamond chain in an external magnetic field are explored using an extended localized-magnon theory complemented by exact diagonalization. We focus on the low-temperature magnetization process, thermodynamic quantities, and magnetocaloric effect in a moderately frustrated regime, where the system hosts a rich variety of unconventional quantum phases including the uniform and cluster-based Haldane states, the fully fragmented monomer-dimer phase, and the bound-magnon crystal preceding the full magnetic saturation. The localized-magnon approach elaborated in our recent work is extended here to account for the uniform Haldane phase, thereby allowing the lattice-gas description to be generalized from the highly frustrated to the moderately frustrated regime. The resulting monomer-dimer lattice-gas model captures anomalous features of the magnetization, susceptibility, entropy, specific heat, and magnetic Grüneisen parameter near field-driven transitions between the quantum phases manifested as zero, one-sixth, one-third, and two-thirds magnetization plateaus.