Magnetism in a distorted kagome lattice: the case of Y-kapellasite

Compounds like the well-known Herbertsmithite are examples  of the ideal spin-1/2 antiferromagnetic (AFM) kagome lattice which has one of the most interesting magnetic phase diagrams. However, while the perfect AFM kagome lattice has been extensively investigated, less is known about distorted kagome lattices.

Here we focus on an unexplored distorted spin-1/2 kagome lattice with three symmetry-inequivalent nearest-neighbor AFM Heisenberg couplings. The recently synthesized Y-kapellasite Y₃Cu₉(OH)₁₉Cl₈ is a realization of such a distorted lattice. First, we analyse the classical magnetic phase diagram using analytical arguments and numerical methods, and find a rich classical phase diagram with a Q=0 magnetic phase, Q=(1/3,1/3) non-collinear coplanar magnetic phases and a classical spin liquid regime. In a second step we estimate the effective magnetic Heisenberg Hamiltonian by total-energy mapping analysis within the FPLO framework. Using the extracted Heisenberg Hamiltonian we predict Y-kapellasite to be localized in the Q=(1/3,1/3) phase which is stable after inclusion of quantum effects.