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Iron(II) spin crossover (SCO) complexes indicate a reversible transition from the low-spin state (LS, S=0) to a high-spin state (HS, S=2) by e.g. variation of temperature, pressure or by irradiation with light [1]. Therefore, these materials are promising candidates for information storage [2]. However, practical device applications require thin films with these properties.
The SCO-compound [Fe(Htrz)2(trz)] (BF4) (1) switches between the LS and the HS state with a 30 K wide thermal hysteresis loop above room temperature [3]. We prepared thin films of 1 on a SiO2 substrate by spin coating. The spin states of the films were characterized by Mössbauer spectroscopy in reflection mode using a MIMOS II spectrometer. A low quadrupole splitting (LS state) at 300 K and a high quadrupole splitting (HS state) at 400 K were found for the films, as well as for bulk powder of 1. This confirms a LS – HS transition above room temperature. Furthermore, synchrotron based nuclear resonance scattering measurements from 80 K to 400 K indicate that the hyperfine parameters as well as the Fe-vibrational density of states of the film are similar to those of the bulk powder of 1. These studies show that the SCO films prepared by spin coating have similar SCO properties as the bulk complex.
[1] P. Gütlich, et al., Angew. Chem. 106, (1994), 2109-2141
[2] J. Kröber, et al., Chem. Mater. 6, (1994), 1404-1412
[3] F. Guillaume, et al., Chemical Physics Letters 604, (2014), 105-109
