Observation of Two-Step Spin Transition in Graphene Oxide-Based Hybrids with Iron(II) 4-amino-1,2,4-triazole Spin Crossover Nanoparticles.

A novel experimental protocol based on a reverse micellar method is presented for the synthesis of graphene oxide (GO)-based hybrids with spin crossover nanoparticles (SCO NPs) of the 1D iron(II) coordination polymer with the formula Fe(NHtrz). By introducing different quantities of 0.5% and 1.0% of GO (according to iron(II)) into the aqueous phase, two hybrids, and , were synthesized, respectively. The morphological homogeneity of the NPs on the surface of the GO flakes is greatly improved in comparison to the pristine Fe(NHtrz) NPs. From the magnetic point of view and at a low magnetic sweep rate of 1 K/min, a two-step hysteretic behavior is observed for and , where the onset of the low-temperature second step appeared at 40% and 30% of the HS fraction, respectively. For faster sweep rates of 5-10 K/min, the two steps from the cooling branch are progressively smeared out, and the critical temperatures observed are T↑ = 343 K and T↓ = 288 K, with a thermal width of 55 K for both and . A Raman laser power-assisted protocol was used to monitor the thermal tolerance of the hybrids, while XPS analysis revealed electronic interactions between the SCO NPs and the GO flakes.