Microscopic spin interactions on a deformed Kagomé lattice of volborthite are investigated through magnetoelastic couplings. A negative longitudinal magnetostriction ∆L < 0 in the b axis is observed, which depends on the magnetization M with a peculiar relation of ∆L/L ∝ M1.3. Based on the exchange striction model, it is argued that the negative magnetostriction originates from a pantograph-like lattice change of the Cu-O-Cu chain in the b axis, and that the peculiar dependence arises from the local spin correlation. This idea is supported by DFT+U calculations simulating the lattice change and a finite-size calculation of the spin correlation, indicating that the recently proposed coupled-trimer model is a plausible one.
|Publication status||Published - 2019 Mar 12|
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