Controlling the Kinetics of Spin Transitions through Heterostructure Elasticity*

An often overlooked feature of spin transitions is the significant volume change associated with altered metal-ligand bonding between the two spin states. Recent examples of exploiting the strain developed during a spin transition include integration into hybrid materials to influence electrical, optical, or magnetic properties. These applications all require the spin transition material to physically couple to other components; however, an interface with another material can strongly influence the behavior of the spin transition material, especially as sizes approach the nanoscale. Our lab has shown these interfaces can dramatically influence the kinetics of solid-state spin transitions. For example, the rate of the light-induced spin transition in Rb_xCo[Fe(CN)₆]_y (RbCoFe-PBA) increases by several orders of magnitude when RbCoFe-PBA is used as the core of a core-shell particle, relative to uncoated RbCoFe-PBA. A theoretical electroelastic model was used to guide chemical alterations, allowing the mechanism to be probed experimentally with nuclear inelastic scattering.