Magnetic Order and Other Phase Transitions in Mixed-Valent YbPd

Specific heat, thermal expansion, and electrical resistivity show that YbPd undergoes four phase transitions at 0.5, 1.9, 105, and 125 K. From magnetic-susceptibility measurements the transition at 0.5 K is found to be magnetic. The quasielastic magnetic linewidth is large as usual for mixed valence, but decreases with temperature and is smaller than $k_{\mathrm{B}}T$ everywhere. The magnetic order of YbPd occurs at a fractional Yb valence of $v=2.8\mathrm{}$ (measured by $L_{\mathrm{III}}$ absorption), i.e., near configurational crossover of $4f^{13}$ and $4f^{14}$.