Authors: Jiang, XY; Hao, GH; Wang, X; Mosey, A; Zhang, X; Yu, L; Yost, AJ; DiChiara, AD; N'Diaye, AT; Cheng, XM; Zhang, J; Cheng, RH; Xu, XS; Dowben, PA
Publication Type: Journal Article
Source: JOURNAL OF PHYSICS-CONDENSED MATTER, 31 (31):10.1088/1361-648X/ab1a7d AUG 7 2019
Abstract: 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 157K. 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.