Abstract
Microwave electromagnetic radiation that ranges from one meter to one millimetre wavelengths is finding numerous applications for wireless communication, navigation and detection, which makes materials able to tune microwave radiation getting widespread interest. Here we offer a new way to tune GHz frequency radiation by using spin-crossover complexes that are known to change their various physical properties under the influence of diverse external stimuli. As a result of electronic re-configuration process, microwave absorption properties differ for high spin and low spin forms of the complex. The evolution of a microwave absorption spectrum for the switchable compound within the region of thermal transition indicates that the high-spin and the low-spin forms are characterized by a different attenuation of electromagnetic waves. Absorption and reflection coefficients were found to be higher in the high-spin state comparing to the low-spin state. These results reveal a considerable potential for the implementation of spin-crossover materials into different elements of microwave signal switching and wireless communication.
Highlights
In recent years, a rapid increase in the use of wireless communication tools, digital systems, local area networks, and other equipment, which uses electromagnetic waves in the GHz range, is observed
In this work a class of bistable compounds in perspective of electromagnetic signals control, so called, spin-crossover (SCO) complexes, is analysed. They represent a group of compounds which can undergo spin transition under the influence of such external stimuli as temperature[17] or pressure[18], light irradiation[19], magnetic field[20] or adsorption of guest molecules[21]
All possibilities of application for these materials are driven by the variation of a whole set of their physical characteristics when the spin state changes
Summary
Shirt-circuit line method, which is a powerful tool to determine dielectric properties of a material, was used to measure SCO induced switch of the refractive index and the absorption factor of 1. There is a slight decrease of refraction index with temperature (Fig. 4b) in the region where no spin transition is observed which is caused by the thermal expansion of the complex. Due to the hysteresis of spin transition, dielectric properties of the complex are different in heating and cooling modes that causes a memory effect (in this case – an ability to possess different values of refractive index in the same conditions depending on how this state has been reached). Because spin transition occurs on the nanosecond scale[45], microwave switches based on SCO compounds can become a new route towards ultrafast modulation of microwave radiation
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