Abstract-Terahertz frequency spectrum analysis with a nanoscale antiferromagnetic tunnel junction

Journal of Applied Physics

Sulymenko,  S. Louis, J. Li,  R. S. Khymyn, E. Bankowski,  T. Meitzler,  V. S. Tyberkevych,  A. N. Slavin,  O. V. Prokopenko,

(a) Pt/AFM/MgO/Pt antiferromagnetic tunnel junction (ATJ). The driving dc current Idrive(t)$I_{\mathrm{drive}}(t)$ flowing in the bottom Pt layer of an ATJ generates the transverse spin current ISH$I_{\mathrm{SH}}$ flowing into the AFM layer, which excites the TF rotation of magnetization of the AFM sublattices and, consequently, the TF variations of the junction resistance R(t)$R(t)$. When a TF signal with power Ps$P_s$ and frequency fs$f_s$ is supplied to the junction, its action results in the generation of voltage Uatj$U_{\mathrm{atj}}$ across the whole structure. (b) A simplified equivalent electric scheme of the ATJ-based detector connected through an ideal bias tee to a source of an external TF signal.

https://aip.scitation.org/doi/10.1063/1.5140552

A method to perform spectrum analysis on low power signals between 0.1$0.1$ and 10 THz is proposed. It utilizes a nanoscale antiferromagnetic tunnel junction (ATJ) that produces an oscillating tunneling anisotropic magnetoresistance, whose frequency is dependent on the magnitude of an evanescent spin current. It is first shown that the ATJ oscillation frequency can be tuned linearly with time. Then, it is shown that the ATJ output is highly dependent on matching conditions that are highly dependent on the dimensions of the dielectric tunneling barrier. Spectrum analysis can be performed by using an appropriately designed ATJ, whose frequency is driven to increase linearly with time, a low pass filter, and a matched filter. This method of THz spectrum analysis, if realized in the experiment, will allow miniaturized electronics to rapidly analyze low power signals with a simple algorithm. It is also found by simulation and analytical theories that for an ATJ with a 0.09μm2$0.09\mu {\mathrm{m}}^2$ footprint, spectrum analysis can be performed over a 0.25THz$0.25\mathrm{THz}$ bandwidth in just 25 ns on signals that are at the Johnson–Nyquist thermal noise floor.

Abstract-Terahertz-Frequency Spin Hall Auto-oscillator Based on a Canted Antiferromagnet

O. R. Sulymenko, O. V. Prokopenko, V. S. Tiberkevich, A. N. Slavin, B. A. Ivanov, and R. S. Khymyn

https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.8.064007

We propose a design of a terahertz-frequency signal generator based on a layered structure consisting of a current-driven platinum (Pt) layer and a layer of an antiferromagnet (AFM) with easy-plane anisotropy, where the magnetization vectors of the AFM sublattices are canted inside the easy plane by the Dzyaloshinskii-Moriya interaction (DMI). The dc electric current flowing in the Pt layer creates due to the spin Hall effect, a perpendicular spin current that, being injected in the AFM layer, tilts the DMI-canted AFM sublattices out of the easy plane, thus exposing them to the action of a strong internal exchange magnetic field of the AFM. The sublattice magnetizations, along with the small net magnetization vector $m_{\mathrm{DMI}}$ of the canted AFM, start to rotate about the hard anisotropy axis of the AFM with the terahertz frequency proportional to the injected spin current and the AFM exchange field. The rotation of the small net magnetization $m_{\mathrm{DMI}}$ results in the terahertz-frequency dipolar radiation that can be directly received by an adjacent (e.g., dielectric) resonator. We demonstrate theoretically that the radiation frequencies in the range $f=0.05–2\mathrm{THz}$ are possible at the experimentally reachable magnitudes of the driving current density, and we evaluate the power of the signal radiated into different types of resonators. This power increases with the increase of frequency $f$, and it can exceed $1\mu W$ at $f\sim 0.5\mathrm{THz}$ for a typical dielectric resonator of the electric permittivity $ϵ\sim 10$ and a quality factor $Q\sim 750$.

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