Effect of Pressure on the Magnetic Properties and Crystal Structure of Gd, Tb, Dy, and Ho

Abstract

X-ray diffraction powder patterns taken at high pressure suggest by analogy to Gd that Tb, Dy, and Ho have first-order transitions from a hcp to a Sm-type structure at high pressure. The $\frac{c}{a}$ ratio of the hcp phases increases with pressure toward the ideal value. The change of the Curie or N\'eel temperature with pressure of Gd, Tb, Dy, and Ho has been measured up to 85 kbar by an ac method in which the sample forms the core of a transformer. The first-order transitions are observed in changes in the magnetic properties. The initial susceptibility shows two new peaks in isobaric temperature cycles made above the transitions. The difference between the ordering temperature of the low- and high-pressure phases near the transition are -37, -21, -12, and -9\ifmmode^\circ\else\textdegree\fi{}K for Gd, Tb, Dy, and Ho, respectively. The change in the Curie point of Gd(I) is -1.72\ifmmode\pm\else\textpm\fi{}0.7\ifmmode^\circ\else\textdegree\fi{}K/kbar. The changes in N\'eel temperature are: Gd(II) -1.46\ifmmode\pm\else\textpm\fi{}0.11, Tb(I) -1.07\ifmmode\pm\else\textpm\fi{}0.03, Tb(II) -0.83\ifmmode\pm\else\textpm\fi{}0.08, Dy(I) -0.66\ifmmode\pm\else\textpm\fi{}0.04, Dy(II) -0.67\ifmmode\pm\else\textpm\fi{}0.07, Ho(I) -0.48\ifmmode\pm\else\textpm\fi{}0.01\ifmmode^\circ\else\textdegree\fi{}K/kbar. The results are compared with other measurements on rare-earth metals.