Browsing by Author "Physics, School of Sciences"

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    Tunable spin-state bistability in a spin crossover molecular complex
    (IOP, 2019) Jiang, Xuanyuan; Hao, Guanhua; Wang, Xiao; Mosey, Aaron; Zhang, Xin; Yu, Le; Yost, Andrew J.; Zhang, Xin; DiChiara, Anthony D.; N'Diaye, Alpha T.; Cheng, Xuemei; Zhang, Jian; Cheng, Ruihua; Xu, Xiaoshan; Dowben, Peter A.; Physics, School of Sciences
    The spin crossover (SCO) transitions at both the surface and over the entire volume of the [Fe{H2B(pz)2}2(bipy)] polycrystalline films on Al2O3 substrates have been studied, where pz  =  pyrazol-1-yl and bipy  =  2,2'-bipyridine. For [Fe{H2B(pz)2}2(bipy)] films of hundreds of nm thick, magnetometry and x-ray absorption spectroscopy measurements show thermal hysteresis in the SCO transition with temperature, although the transition in bulk [Fe{H2B(pz)2}2(bipy)] occurs in a non-hysteretic fashion at 157 K. While the size of the crystallites in those films are similar, the hysteresis becomes more prominent in thinner films, indicating a significant effect of the [Fe{H2B(pz)2}2(bipy)]/Al2O3 interface. Bistability of spin states, which can be inferred from the thermal hysteresis, was directly observed using temperature-dependent x-ray diffraction; the crystallites behave as spin-state domains that coexist during the transition. The difference between the spin state of molecules at the surface of the [Fe{H2B(pz)2}2(bipy)] films and that of the molecules within the films, during the thermal cycle, indicates that both cooperative (intermolecular) effects and coordination are implicated in perturbations to the SCO transition.