Negative permittivity devices or Epsilon- negative (ENG) composites are of great importance in shielding, antennas and nano-optoelectronics applications at GHz frequencies. In recent years, many researchers have study some  ferrite - based materials with metal particles for finding an alternative ENG composites in the fabrication of optoelectronic resonance components, antennas and invisible coating’s industries. In the present work, an attempt has been made to investigate the optical, dielectric and electronic characteristics of the ferrite yttrium-iron-copper garnet matrix (FYICG) with different lithium (Li) nano-particles, synthesized by in situ method at 650-1250 °C and at 80- 120 GHz. The measurement cut-off frequency and modulation, sample morphology (studied with Scanning electron microscopy (SEM)), the other electrical characteristics with using Prova tool and home-set electrical measurement system as well as transmittance and reflection parameters measurement system, could provide a suitable ENG for future of the optoelectronic and electromagnetic devices.