Excitation Spectrum and Superexchange Pathways in the Spin Dimer VODPO_4 . 1/2 D_2O

TL;DR

This study uses inelastic neutron scattering to investigate magnetic excitations in VODPO_4·1/2 D_2O, revealing unexpected superexchange pathways and challenging previous assumptions about its magnetic dimer structure.

Contribution

It identifies an alternative V-V superexchange pathway involving PO_4 groups, revising the understanding of magnetic dimers in VODPO_4·1/2 D_2O.

Findings

Observed a dispersionless magnetic mode at 7.81 meV

V-V separation in magnetic dimers is 4.43 Å, not 3.09 Å

Superexchange occurs through PO_4 groups, not direct V-V pairs

Abstract

Magnetic excitations have been investigated in the spin dimer material VODPO_4 \cdot 1/2 D_2O using inelastic neutron scattering. A dispersionless magnetic mode was observed at an energy of 7.81(4) meV. The wavevector dependence of the scattering intensityfrom this mode is consistent with the excitation of isolated V^{4+} spin dimers with a V-V separation of 4.43(7) \AA. This result is unexpected since the V-V pair previously thought to constitute themagnetic dimer has a separation of 3.09 \AA. We identify an alternative V-V pair as the likely magnetic dimer, which involves superexchange pathways through a covalently bonded PO_4 group. This surprising result casts doubt on the interpretation of (VO)_2P_2O_7 as a spin ladder.