Anomalous Pressure Dependence of magnetic Ordering Temperature in Tb to 141 GPa: Comparison with Gd and Dy

In previous studies the pressure dependence of the magnetic ordering temperature $T_{\text{o}}$ of Dy was found to exhibit a sharp increase above its volume collapse pressure of 73 GPa, appearing to reach temperatures well above ambient at 157 GPa. In a search for a second such lanthanide, electrical resistivity measurements were carried out on neighboring Tb to 141 GPa over the temperature range 3.8 - 295 K. Below Tb's volume collapse pressure of 53 GPa, the pressure dependence $T_{\text{o}}(P)$ mirrors that of both Dy and Gd. However, at higher pressures $T_{\text{o}}(P)$ for Tb becomes highly anomalous. This result, together with the very strong suppression of superconductivity by dilute Tb ions in Y, suggests that extreme pressure transports Tb into an unconventional magnetic state with an anomalously high magnetic ordering temperature.