Spin-State Ice - Dr Jace Cruddas

Spin crossover molecules have two possible spin-states: one high-spin and one low-spin. A change spin-state is accompanied by drastic changes in the molecular volume, which in turn gives rise to elastic interactions in molecular frameworks and materials, and can lead to collective phenomena including hysteresis, multistep transitions, and the antiferroelastic order of spin states.[1] We propose that on frustrated lattices elastic interactions can give rise to a new phase of matter, spin-state ice, so-called in analogy to water-ice and spin-ice. This phase lacks any long-range ordering of spin-states; instead local clusters of molecules follow an “ice rule”, for example on the Kagome lattice each triangle must contain two metal centres in one spin state and one in the other. The existence of these ice rules gives rise to a `smoking gun' piece of evidence - distinct pinch point correlations in the neutron scattering structure factor, and distinct signatures in the electron paramagnetic resonance, and thermodynamic experiments.[2,3] Additionally, we show that spin-state ice supports mobile collective excitations that carry a fraction of the spin of the constituent molecules, but no electrical charge.[2,3]

References:

[1] P. Gütlich, H. A. Goodwin, Topics in Current Chemistry; Springer-Verlag:Berlin, 233, 234-235 (2004)

[2] J. Cruddas, B. J. Powell, J. Am. Chem. Soc, 141, 19790-19799 (2019)

[3] J. Cruddas, B. J. Powell, Phys. Rev. B., 104, 024433 (2021)