Flexible magnetism in flexible crystals*

We predict that the elastically flexible crystal, [Cu(acac)₂] [1], contains quasi-one-dimensional magnetic interactions that change dramatically when the crystal is bent. In the unbent crystal, all interchain interactions are doubly frustrated – geometrically and by the equipoise of antiferromagnetic and ferromagnetic interactions in the two planes perpendicular to the chains. We parametrize a Heisenberg model for the unbent and bent crystal from broken-symmetry density functional theory [2], revealing that the intrachain exchange interaction is an order of magnitude larger than the interchain exchange interactions. We calculate the three dimensional Néel temperature, T_N, from the chain random phase approximation (CRPA) [3], which reveals that [Cu(acac)₂] is an almost perfect Tomonaga-Luttinger liquid (TLL) with a T_N that increases by approximately 175 orders of magnitude when the material is bent. This is a proof of principle demonstration that magnetic properties can be significantly altered by bending flexible crystals.

[1] Worthy, A. et al. Nat. Chem. 2017,10, 65–69.
[2] Noodleman, L. J. Chem. Phys. 1981, 74, 5737–5743.
[3] Bocquet, M. et al. Phys. Rev. B. 2001, 64, 094425.