# Theory of Antiferromagnet-Based Detector of Terahertz Frequency Signals

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## Abstract

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## 1. Introduction

## 2. Physical Structure

## 3. Magnetization Precession Induced by a Polarized THz EM Signal

- (a) Easy-axis uniaxial AFM (${H}_{\mathrm{HA}}=0$).

- (b) Easy-plane biaxial AFM (${H}_{\mathrm{HA}}\ne 0$).

## 4. Rectification of THz-Frequency Electromagnetic Signals

- (a) Easy-axis uniaxial AFM (${H}_{\mathrm{HA}}=0$).

- (b) Easy-plane biaxial AFM (${H}_{\mathrm{HA}}\ne 0$).

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**(

**a**) Schematic view of the resonance detector based on an AFM/HM heterostructure under the action of a THz-frequency electromagnetic signal with controllable polarization. Here $\mathbf{l}$(t) is the Neel vector oriented along the anisotropy easy-axis, ${V}_{\mathrm{OUT}}$ is the output DC electric voltage, and ${\mathbf{H}}_{\mathbf{0}}$ is the external DC bias magnetic field; (

**b**) dependence of the resonance frequencies of the detector based on the uniaxial AFM MnF${}_{2}$ on the DC bias magnetic field ${H}_{0}$ for ${\mathbf{H}}_{0}\Vert {\mathbf{e}}_{\mathrm{EA}}$ and ${\mathbf{H}}_{0}\perp {\mathbf{e}}_{\mathrm{EA}}$.

**Figure 2.**AFM detector sensitivity as a function of the external signal frequency (

**a**,

**c**) and bias magnetic field (

**b**,

**d**) for the AFM-HM heterstructures containing uniaxial ($Mn{F}_{2}$) and biaxial ($NiO$) AFM crystals. Calculation were performed for the lowest-frequency AFMR modes).

Material | ${\mathit{H}}_{\mathbf{EA},\mathbf{HA}}$, T | ${\mathit{H}}_{\mathbf{ex}}$, T | f${}_{\mathit{AFMR}}$, GHz | $\mathbf{\Delta}$f, GHz | ${\mathit{V}}_{\mathit{ISHE}}$, nV | Ref. |
---|---|---|---|---|---|---|

FeF${}_{2}$ | 20 | 108 | 1400 | 30 | - | [26,27] |

Cr${}_{2}$O${}_{3}$ | 0.07 | 490 | 163 | 5.6 | 30 | [15,17] |

MnF${}_{2}$ | 0.85 | 106 | 245 | 2.6 | 60 | [14,16] |

NiO | 0.03, 0.7668 | 1937 | 220, 1100 | 18 | - | [28,29] |

**Table 2.**Expressions for the eigen-frequencies ${\omega}_{\pm}$ and AFM diode sensitivity R at different orientations of the external bias magnetic field ${\mathbf{H}}_{0}$ relative to the easy axis ${\mathbf{e}}_{\mathrm{EA}}$ of the AFM layer and polarizations (LP or CP) of the external EM signal for the uniaxial AFM crystal. The numbers in parentheses (·) correspond to the equation numbers in the main text of the paper.

Parameter | ${\mathbf{H}}_{0}=0$ | ${\mathbf{H}}_{0}\Vert {\mathbf{e}}_{\mathbf{EA}}$ | ${\mathbf{H}}_{0}\perp {\mathbf{e}}_{\mathbf{EA}}$ |
---|---|---|---|

${\omega}_{\pm}$ | $\sqrt{{\omega}_{\mathrm{ex}}{\omega}_{\mathrm{EA}}}$ | $\sqrt{{\omega}_{\mathrm{ex}}{\omega}_{\mathrm{EA}}}\pm {\omega}_{\mathrm{H}}$ | $\sqrt{{\omega}_{\mathrm{ex}}{\omega}_{\mathrm{EA}}}$, $\sqrt{{\omega}_{\mathrm{ex}}{\omega}_{\mathrm{EA}}+{\omega}_{\mathrm{H}}^{2}}$ |

${R}_{\mathrm{LP}}$ | 0 | (24) | 0 |

${R}_{\mathrm{CP}}$ | (25) | (25) | (25) |

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**MDPI and ACS Style**

Safin, A.; Nikitov, S.; Kirilyuk, A.; Tyberkevych, V.; Slavin, A.
Theory of Antiferromagnet-Based Detector of Terahertz Frequency Signals. *Magnetochemistry* **2022**, *8*, 26.
https://doi.org/10.3390/magnetochemistry8020026

**AMA Style**

Safin A, Nikitov S, Kirilyuk A, Tyberkevych V, Slavin A.
Theory of Antiferromagnet-Based Detector of Terahertz Frequency Signals. *Magnetochemistry*. 2022; 8(2):26.
https://doi.org/10.3390/magnetochemistry8020026

**Chicago/Turabian Style**

Safin, Ansar, Sergey Nikitov, Andrei Kirilyuk, Vasyl Tyberkevych, and Andrei Slavin.
2022. "Theory of Antiferromagnet-Based Detector of Terahertz Frequency Signals" *Magnetochemistry* 8, no. 2: 26.
https://doi.org/10.3390/magnetochemistry8020026