Magnetic Ordering at Anomalously High Temperatures in Dy at Extreme Pressures: a New Kondo-Lattice State?

In an attempt to destabilize the magnetic state of the heavy lanthanides Dy and Gd, extreme pressures were applied in an electrical resistivity measurement to 157 GPa over the temperature range 5 - 295 K. The magnetic ordering temperature $T_{\text{o}}$ and spin-disorder resistance $R_{sd}$ of Dy, as well as the superconducting pair-breaking effect $\Delta T_{c}$ in Y(1 at.\% Dy), are found to track each other in a highly non-monotonic fashion as a function of pressure, all three increasing sharply above 73 GPa, the critical pressure for a 6\% volume collapse in Dy. At 157 GPa $T_{\text{o}}$ is estimated to reach temperatures in the range 370 - 500 K, the highest magnetic ordering temperature of any lanthanide. In contrast, $T_{\text{o}% }(P)$ for Gd shows no such sharp increase to 105 GPa. Taken together, these results suggest that pressures greater than 73 GPa transform Dy from a conventional magnetic lanthanide into a Kondo lattice system with an anomalously high magnetic ordering temperature.