Coupled frustrated quantum spin-1/2 chains with orbital order in volborthite Cu3V2O7(OH)2•2H2O

We present a microscopic magnetic model for the spin-liquid candidate volborthite Cu3V2O7 (OH)(2)center dot 2H(2)O. The essentials of this density-functional-theory-based model are (i) the orbital ordering of Cu(1) 3d(3z2-r2) and Cu (2) 3d(x2-y2), (ii) three relevant couplings J(ic), J(1), and J(2), (iii) the ferromagnetic nature of J(1), and (iv) frustration governed by the next-nearest-neighbor exchange interaction J(2). Our model implies magnetism of frustrated coupled chains in contrast to the previously proposed anisotropic kagome model. Exact diagonalization studies reveal agreement with experiments.