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Faculty Publication: Associate Professor of Physics Xuemei May Cheng

June 13, 2019

Tunable spin-state bistability in a spin crossover molecular complex

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. 

Department of Physics