THz Spectrum Analysis Using an Antiferromagnetic Tunnel Junction as a Signal Mixer

We propose a novel, all-electrical method of performing spectrum analysis between 0.1 THz to 1.0 THz (in the “THz gap”). The method features an antiferromagnetic (AFM) tunnel junction that consists of 4 thin layers (Pt, AFM, MgO, Pt) and functions as follows [1]. First, an in-plane dc bias current I(t) in the Pt layer creates perpendicular spin Hall current, which excites rotation of the AFM sublattices with a frequency f(t) ~ I(t). When the bias current I(t) increases with time, f(t) can be linearly swept over the THz gap. Due to the tunneling magnetoresistance effect, the resistance R(t) of the MgO/Pt structure oscillates with the same frequency f(t). Oscillating resistance R(t) is mixed with an input signal producing low-frequency output voltage V(t) that temporally encodes the input spectrum. The spectrum can be extracted from V(t) using signal processing method described in [2].

[1] O.R. Sulymenko, et al., "Terahertz-Frequency Signal Source Based on an Antiferromagnetic Tunnel Junction", IEEE Magnetics Letters 9, 1 (2018).
[2] S. Louis, et al., "Ultra-fast wide band spectrum analyzer based on a rapidly tuned spin-torque nano-oscillator", Appl. Phys. Lett. 113, 112401 (2018).