The magnetic field effect of the covalent bond between atoms is generally small because the magnetic field available in a laboratory is typically around 10 T, and its Zeeman energy is much smaller than the bonding energy. However, the covalency of a specific chemical bond in ferroelectric is affected by a temperature change near the transition temperature ($T_{\mathrm{c}}$). Namely, the ion position shifts, and electrical polarization appears, which can be regarded as a phenomenon that occurs by changing the covalency of a specific chemical bond. Since the chemical bond generally becomes soft in the vicinity of the $T_{\mathrm{c}}$, we may have a chance to observe a significant magnetic field effect on the covalency in ferroelectrics if the magnetic field is strong enough.

Recently, several new techniques for measurements in ultrahigh magnetic fields exceeding 100 T have been developed [1-7]. One of them is on the measurement of the dielectric constant [7]. Here, we introduce the technique for the dielectric measurement and a preliminary result on the dielectric constant of an archetypal ferroelectric BaTiO₃.

Figure 1 shows the schematic diagram of the dielectric constant measurement in ultrahigh magnetic fields exceeding 100 T. The single-turn coil magnetic field generator at ISSP, UTokyo, was used to generate a magnetic field of up to 120 T for the present work. The radio frequency (RF) modulated electromagnetic wave (34 MHz) is introduced to the sample, and the transmission signal is recorded by the oscilloscope. The recorded RF data is modulated by the change in the sample dielectric constant. The sample temperature is controlled by a hand-made heater and is measured by a thermocouple placed near the sample.

The single crystal of BaTiO₃ was used for the experiment. The $T_{\mathrm{c}}$ was found to be near 393 K. Before the high magnetic field experiment, the electrical polarization ($P$) direction was forced to be aligned by the poling process with the application of high voltage.

The result of the magnetic field dependence of the dielectric constant ($\epsilon$) is shown in Fig. 2. The RF signal detected is converted to $\epsilon$ through the calibration curve that is obtained by the temperature dependence of the dielectric constant of the sample.

The dielectric constant decreases by a magnetic field ($B$) when the field exceeds near 100 T. We confirmed that similar results are obtained whenever the $B$ is parallel to the $P$ and the temperature is close to $T_{\mathrm{c}}$. However, there appears to be no reduction of the ε appears in high magnetic fields when $B\perp P$ or the temperature is far from $T_{\mathrm{c}}$ [7]. Currently, one of the possible explanations is an enhancement of the covalency and resultant stabilization of the ferroelectric phase by a magnetic field. Further studies in the future will elucidate the origin of the field-induced change in $\epsilon$.

References

• [1] S. Takeyama, R. Sakakura, Y. H. Matsuda, A. Miyata, and M. Tokunaga., J. Phys. Soc. Jpn. 81, 014702 (2012).
• [2] A. Ikeda T. Nomura, Y. H. Matsuda, S. Tani, Y. Koba-yashi et al., Rev. Sci. Instrum. 88, 083906 (2017).
• [3] T. Nomura, A. Hauspurg, D. I. Gorbunov, A. Miyata, E. Schulze et al., Rev. Sci. Instrum. 92, 063902 (2021).
• [4] D. Nakamura, M. M. Altarawneh, and S. Takeyama, Meas. Sci. Technol. 29, 035901 (2018).
• [5] T. Shitaokoshi S. Kawachi, T. Nomura et al., Rev. Sci. Instrum. 94, 094706 (2023).
• [6] S. Peng X-G. Zhou, Y. H Matsuda, Q. Chen et al., Supercond. Sci. Technol. 38, 075012 (2025).
• [7] P. Chiu Y. Ishii, and Y. H. Matsuda, J. Appl. Phys. 137, 155903 (2025).

Authors

• P. Chiu, Y Ishii, and Y. H. Matsuda