Tailoring THz antiferromagnetic resonance of NiO by cation substitution

Antiferromagnets generally have a quite high magnetic resonance, as known as the antiferromagnetic resonance, whose frequency goes up to the THz range. They are one of the few materials that can magnetically couple to THz electromagnetic waves and are therefore important materials for THz technologies. In this work, we demonstrate that the THz resonance properties, such as resonant frequency and the $Q$ factor, of antiferromagnetic NiO can be controlled over a wide range by substituting the $\mathrm{N}{\mathrm{i}}^{2+}$ cation with various different cations. Our discussion extends to the trends of how different substitute cations $\mathrm{M}{\mathrm{n}}^{2+}, \mathrm{L}{\mathrm{i}}^{+}$, and $\mathrm{M}{\mathrm{g}}^{2+}$ impact the resonant properties, which suggests a guideline for designing antiferromagnetic THz materials.

Figure 1

(a) Crystalline and magnetic structure of NiO with a cation substitution indicated with the red ion. (b) Schematic illustration of the THz transmission measurement on an antiferromagnet sample. Persistent magnetization dynamics is excited at the antiferromagnetic resonant frequency and therefore the THz waves are absorbed. The x-ray diffraction for (c) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{M}{\mathrm{n}}_x\mathrm{O}$, (d) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{L}{\mathrm{i}}_x\mathrm{O}$, and (e) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{M}{\mathrm{g}}_x\mathrm{O}$. Peaks due to the pure NiO are indexed. Other peaks labeled by * are due to impurity phases of $\mathrm{MnN}{\mathrm{i}}_2{\mathrm{O}}_4$.

Figure 2

Transmission of the THz wave as functions of frequency and temperature for (a) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{M}{\mathrm{n}}_x\mathrm{O}$, (b) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{L}{\mathrm{i}}_x\mathrm{O}$, and (c) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{M}{\mathrm{g}}_x\mathrm{O}$ with various $x$.

Figure 3

Temperature dependence of the resonant frequency for (a) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{M}{\mathrm{n}}_x\mathrm{O}$, (b) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{L}{\mathrm{i}}_x\mathrm{O}$, and (c) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{M}{\mathrm{g}}_x\mathrm{O}$ with various $x$.

Figure 4

${\omega }_0/\left(2\pi \right)$ and $T_N$ as a function of composition $x$ for (a) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{M}{\mathrm{n}}_x\mathrm{O}$, (b) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{L}{\mathrm{i}}_x\mathrm{O}$, and (c) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{M}{\mathrm{g}}_x\mathrm{O}$.

Figure 5

The transmission spectra at 300 K for (a) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{M}{\mathrm{n}}_x\mathrm{O}$, (b) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{L}{\mathrm{i}}_x\mathrm{O}$, and (c) $\mathrm{N}{\mathrm{i}}_{1-x}\mathrm{M}{\mathrm{g}}_x\mathrm{O}$. The arrows indicate the position of the absorption peaks (d) $\mathrm{\Delta }\omega /\left(2\pi \right)$ and the $Q$ factor as a function of composition $x$. ($✧$) denotes the pure NiO. The dotted curves are a guide for the eye.