Coupling Nanostructured CsNiCr Prussian Blue Analogue to Resonant Microwave Fields

Collective spin excitations in magnetically ordered materials are exploited for advanced applications in magnonics and spintronics. In these contexts, conditions for minimizing dissipative effects are sought in order to obtain long living excitations that can be coherently manipulated. Organic and coordination magnetic materials may offer alternative options for their flexibility and low spin-orbit effects. Likewise, ferromagnetic nanostructures provide a versatile platform for hybrid architectures, yet downsizing affects the dynamics of magnetic excitations and needs to be controlled. Here we report a systematic investigation on insulating CsNiCr Prussian blue analogue with different degree of nanostructuring. Combining complementary microwave spectroscopic techniques, we performed magnetic resonance in a wide temperature range across the bulk ferromagnetic transition occurring at TC=90 K. This allows us to monitor key parameters of the spin dynamics through different types of nanostructured samples. We found that, below TC, the Gilbert damping parameter of 10 nm nanoparticles compares well (10-3) with values reported for prototypical inorganic analogues (YIG). Strong coupling with the microwave field of a planar microstrip resonator is then observed for bulk CsNiCr as well as for mutually interacting NPs. These results clarify conditions for the coherent manipulation of collective spin degrees of freedom in nanostructured coordination materials.