Possible Kondo-Lattice-Enhanced Magnetic Ordering at Anomalously High Temperature in Nd Metal under Extreme Compression*

Most elemental lanthanides order magnetically at temperatures $T_{o}$ well below ambient, the highest being 292 K for Gd. Sufficiently high pressure is expected to destabilize the well localized magnetic 4$f$ state of the heavy lanthanides, leading to increasing influence of Kondo physics on the RKKY interaction. For pressures above 80 GPa, $T_{o}$ for Dy and Tb begins to increase dramatically, extrapolating for Dy to a record-high value near 400 K at 160 GPa.\footnote{J. Lim G. Fabbris, D. Haskel, J. S. Schilling, Phys. Rev. B 91, 045116 & 174428 (2015).} This anomalous increase may be an heretofore unrecognized feature of the Kondo lattice state; if so, one would expect $T_{o}$ to pass through a maximum and fall rapidly at even higher pressures. A parallel is suggested to the ferromagnet CeRh$_{3}$B$_{2}$ where $T_{o}=$ 115 K at ambient pressure, a temperature more than 100-times higher than anticipated from simple de Gennes scaling.\footnote{S. A. Shaheen, J. S. Schilling, R. N. Shelton, Phys. Rev. B 31, 656(R) (1985).} Here we discuss recent experiments on Nd where anomalous behavior in $T_{o}(P)$ is found to occur at lower pressures, perhaps reflecting the fact that Nd's 4$f$ wave function is less localized.