Dielectric Transition-Instigated\nExtraordinary Capacitance\nChange with Successive Switching in Loss Tangent at the Spin Transition\nTemperatures of a Spin-Crossover Nanomaterial

The\nmagnetic transition in spin-crossover (SCO) materials\nwith\ntemperature is a dynamic and reversible process, in which the transition\nmetal ions change from a low spin (LS) state to a high spin (HS) state.\nThis work reports extraordinary dielectric transitions at 342 and\n382 K reflected in a capacitance fabricated with a Fe-based SCO material.\nThese transitions are predominantly instigated in its nanomaterial\nphase in thin film-based devices. However, similar devices fabricated\nwith bulk material did not show any significant changes. The associated\ndielectric transitions occur at the magnetic transition temperature\nwithout following their transition sequence. We observed an extraordinary\nshift in capacitance (Δ<i>C</i>) at the transition\ntemperature of about 1100 nF/cm<sup>2</sup>, which is remarkable.\nAdditionally, over a 10<sup>5</sup>-fold enhancement in capacitance\nper unit volume is observed in devices fabricated with nanomaterial\ncompared to those made with bulk powder. Such noteworthy changes could\nbe due to the interface-induced agglomeration of the SCO nanomaterial\nat a macroscopic length scale within the 200 nm thick film and the\npolarization of counterions within the two-dimensional confined structures.\nMore significantly, successive switching in the loss tangent from\nhigh to low and vice versa is observed, widening the applications\nof SCO materials in emerging directions.