Data for Anomalous magnetic exchange in a dimerized quantum magnet composed of unlike spin species

An applied magnetic field of μ0Hc1 = 13.1(1)T is found to close the singlet-triplet energy gap, the magnitude of which is governed by the antiferromagnetic intradimer, J0 ≈ 21 K, and interdimer, J′ ≈ 1 K, exchange energies, determined from magnetometry and electron-spin resonance measurements.

The results of density functional theory (DFT) calculations are consistent with the experimental results. The DFT calculations predict antiferromagnetic coupling along all nearest-neighbor bonds, with the magnetic ground state comprising spins of different species aligning antiparallel to one another, while spins of the same species are aligned parallel. The magnetism in this system cannot be accurately described by the overlap between localized V orbitals and magnetic Cu orbitals lying in the Jahn-Teller (JT) plane, with a tight-binding model based on such a set of orbitals incorrectly predicting that interdimer exchange should be dominant.