A comparative study of electronic, structural, and magnetic properties ofα-,β-, andγ−Cu2V2

We have carried out a detailed first-principles study of the copper pyrovanadate ${\mathrm{Cu}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$ which crystallizes in at least three different polymorphs $\ensuremath{\alpha}, \ensuremath{\beta}$, and $\ensuremath{\gamma}$. The magnetic properties of these systems are analyzed by calculating various exchange interactions and deriving the relevant spin Hamiltonian. Our detailed analysis based on the derived spin model suggests the crucial role of the crystal structure in governing the electronic and magnetic properties of the three different phases of the system. In particular, our calculations reveal that a subtle difference in the crystal structure has a substantial impact on the magnetic properties of the $\ensuremath{\alpha}$ phase. The important role of spin-orbit coupling (SOC) is also investigated for the three different phases of ${\mathrm{Cu}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$. Although SOC stabilizes magnetic order in all the phases, the absence of inversion symmetry leads to an appreciable Dzyaloshinski-Moriya interaction in the $\ensuremath{\alpha}$ phase which in turn causes the canting of the spins and adds to the stabilization of the long-range order. Finally, from the symmetry analysis and total energy calculation we have obtained the magnetic ground state for the different phases of ${\mathrm{Cu}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$. While the symmetry-allowed magnetic ground states for the $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ phases are in agreement with the experimental observations, the theoretically predicted magnetic ground state for the $\ensuremath{\gamma}$ phase is found to be a realization of a dimeric system with the potential to host novel physics.