Interfacial Influence on Elastic Properties of Spin-Transition Nanoparticles

In photo-excited Rb_xCo[Fe(CN)₆]_y@K_aNi[Cr(CN)₆]_b core@shell spin-transition nanoparticles, the rate of the relaxation in the core is accelerated by more than an order of magnitude due to the presence of the shell [1]. In addition, the relaxation rate continues accelerating with increasing shell thickness, which an electro-elastic model explains as a change in the mechanical properties of the core due to its interface with an increasingly rigid shell [1,2]. Here, nuclear inelastic scattering (NIS) was used to study a series of heterostructures with different shells and selectively determine the stiffness of the core, using the low-energy phonon modes and the partial phonon density of states. The results show a significant softening of the low-temperature state in the core with increasing shell thickness, providing a possible explanation for the observed relaxation rate increase. The bulk modulus for each sample was determined using PXRD, and interestingly, shells of different compositions appear to have dissimilar effects on the stiffness of the low-spin state of the core, expected to predominate at low temperatures.
[1] A.C. Felts et al., J. Am. Chem. Soc. 140 (2018) 5814.
[2] A. Slimani et al., Phys. Rev. B 87 (2013) 014111.