Voltage-tunable impedance at a ferromagnetic-semiconductor interface: spectroscopy and applications in reconfigurable spintronics

Abstract This paper presents a comprehensive impedance spectroscopy investigation of Ag/Ni₈₀Fe₂₀/n-Si/Ag heterostructures fabricated via liquid phase epitaxy, revealing profound insights into the electrical and interface properties of ferromagnetic-metal/semiconductor systems. Through multivariable impedance analysis across wide frequency (Hz-MHz), temperature (80–400 K), and bias voltage (− 2 to + 2 V) ranges, we identified complex relaxation processes dominated by interface phenomena at the Ni₈₀Fe₂₀/n-Si junction. The analysis of Nyquist plots, frequency-dependent imaginary impedance, and voltage–temperature characteristics revealed non-ideal diode behavior with ideality factors ranging from 1.5 to 2.3 and barrier heights between 0.68 and 0.82 eV, indicating significant interface inhomogeneity. The extracted parameters demonstrate a strong correlation between temperature-dependent series resistance and interface state density, with an activation energy of approximately 0.12 eV for charge transport. The presence of the ferromagnetic Ni₈₀Fe₂₀ layer introduces unique spin-dependent transport phenomena not observed in conventional metal-semiconductor structures, enabling voltage-tunable impedance and thermally activated relaxation processes. These findings establish fundamental structure–property relationships critical for developing advanced CMOS-compatible spintronic devices, magnetic sensors, and reconfigurable radio-frequency components through tailored interface engineering.