Exchange Interactions and Magnetic Properties of the Layered Vanadates CaV2O5, MgV2O5, CaV3O7, and CaV4O9

Abstract

We have performed ab initio calculations of exchange couplings in the layered vanadates ${\mathrm{CaV}}_2{\mathrm{O}}_5$, ${\mathrm{MgV}}_2{\mathrm{O}}_5$, ${\mathrm{CaV}}_3{\mathrm{O}}_7$, and ${\mathrm{CaV}}_4{\mathrm{O}}_9$. The uniform susceptibility of the Heisenberg model with these exchange couplings is then calculated by the quantum Monte Carlo method; it agrees well with the experimental measurements. Based on our results we naturally explain the unusual magnetic properties of these materials, especially the huge difference in spin gap between ${\mathrm{CaV}}_2{\mathrm{O}}_5$ and ${\mathrm{MgV}}_2{\mathrm{O}}_5$, the unusual long range order in ${\mathrm{CaV}}_3{\mathrm{O}}_7$, and the “plaquette resonating valence bond” spin gap in ${\mathrm{CaV}}_4{\mathrm{O}}_9$.