Low-temperature high-frequency dynamic magnetic susceptibility of classical spin-ice Dy$_2$Ti$_2$O$_7$

TL;DR

This study measures the high-frequency AC magnetic susceptibility of Dy$_2$Ti$_2$O$_7$ across a wide temperature range, revealing temperature and field-dependent magnetic transitions and an unusual low-temperature susceptibility upturn.

Contribution

It provides detailed high-frequency susceptibility data and clarifies the magnetic phase transitions and their frequency independence in Dy$_2$Ti$_2$O$_7$ at low temperatures.

Findings

Peak of susceptibility shifts from 15 K to 45 K at 14.6 MHz.

Reproduction of the spin configuration transition at about 1 T.

Observation of an unusual susceptibility upturn at low temperatures between 1.5 T and 2 T.

Abstract

Radio-frequency (14.6 MHz) AC magnetic susceptibility, $\chi^{\prime}_{AC}$, of \dytio\ was measured using a self-oscillating tunnel-diode resonator. Measurements were made with the excitation AC field parallel to the superimposed DC magnetic field up 5 T in a wide temperature range from 50 mK to 100 K. At 14.6 MHz a known broad peak of $\chi^{\prime}_{AC}(T)$ from kHz - range audio-frequency measurements around 15~K for both [111] and [110] directions shifts to 45~K, continuing the Arrhenius activated behavior with the same activation energy barrier of $E_a \approx 230$~K. Magnetic field dependence of $\chi^{\prime}_{AC}$ along [111] reproduces previously reported low-temperature two-in-two-out to three-in-one-out spin configuration transition at about 1~T, and an intermediate phase between 1 and 1.5~T. The boundaries of the intermediate phase show reasonable overlap with the literature data and connect at a critical endpoint of the first-order transition line, suggesting that these low-temperature features are frequency independent. An unusual upturn of magnetic susceptibility at $T \to 0$ was observed in magnetic fields between 1.5~T and 2~T for both magnetic field directions, before fully polarized configuration sets in above 2~T.