Modifying the cooperative effect of composites [Fe(Htrz)₂(trz)](BF₄) plus polyaniline through the addition of iron magnetite nanoparticles

The high spin state to low spin state transition characteristics of the spin crossover molecule [Fe(Htrz)₂(trz)](BF₄) (where Htrz = 1H-1,2,4-triazole) plus polyaniline can be modified by the addition of iron magnetite (Fe₃O₄) nanoparticles. [Fe(Htrz)₂(trz)](BF₄) exhibits a strong spin state transition from a diamagnet (S=0) to moment paramagnet (S=4) with increasing temperature, but this spin state transition is hysteretic in temperature due to intermolecular interactions - otherwise known as cooperative effects. The temperature dependent hysteresis of the spin state transition decreases, in [Fe(Htrz)₂(trz)](BF₄) polymer thin films, with the addition of polyaniline. This indicates a decrease in the cooperativity in [Fe(Htrz)₂(trz)](BF₄) polymer. Addition of the ferromagnetic Fe₃O₄ nanoparticles leads to a strong superparamagnetic contribution and an increase in the temperature dependent hysteresis of the spin state transition. This suggests that there is not just intermolecular interactions due to strain and steric effects, but also exchange coupling.