Exchange energies of kapellasite from high-temperature series analysis of the kagome lattice J1-J2-Jd-Heisenberg model

We present a method to build magnetic models of insulators based on high-temperature expansions by fitting both the magnetic susceptibility and the low-temperature specific heat data. It is applied to the frustrated magnet kapellasite [Cu3Zn(OH)(6)Cl-2] with the J(1)-J(2)-J(d)-Heisenberg model on the kagome lattice. Experimental data are reproduced with a set of competing exchange energies centered at J(1) = -12, J(2) = -4, and J(d) = 15.6 K, where J(d) is the third-neighbor exchange energy across the hexagon. Strong constraints between these exchange energies are established. These values confirm the results of Fak et al. [Phys. Rev. Lett. 109, 037208 (2012)] regarding the location of kapellasite in the cuboc2 phase of the Heisenberg model. The quality and limits of this modeling are discussed. DOI: 10.1103/PhysRevB.87.155107