Quadrupole order in clathrate compound Pr₃Pd₂₀Si₆

Role of Hyperfine Coupling in Magnetic and Quadrupolar Ordering ofPr3Pd20Si6

“…2 shows the specific heat C measured at zero magnetic field. We observe two distinct peaks at T Q = 0.21 K and T N 1 = 0.14 K, consistent with phase transitions found in previous ultrasound measurements of Pr 3 Pd 20 Si 6 SC [11,12]. These transitions were not ob- served in specific heat data of polycrystalline (PC) samples, prepared by arc-melting and annealing [16].…”

“…5 shows the phase diagram derived from the Tand H-dependence of features in C and χ ′ . The highest temperature phase boundary agrees very well with previous results from measurements of the elastic constants [12]. From the shape of the phase boundary and symmetry arguments, this transition was interpreted as AFQ ordering of O 0 2 = 1 2 (2J 2 z − J 2 x − J 2 y ) moments at the 8c sites, where the Γ 3 ground state does not support a magnetic dipolar order parameter [12].…”

“…The occupancy ratio of 8c:4a is 2:1. Depending on the 8c and 4a CEF ground states, a rich variety of multipolar orders may appear at low temperatures, as witnessed by measurements of the elastic constants [10][11][12], as well as thermodynamic and transport studies [9]. The Pr 3 Pd 20 Si 6 clathrate in- (Color online) (a): Specific heat C(T ) of Pr3Pd20Si6 at B = 0 T, measured for SC (black symbols) and PC samples (gray symbols).…”

Quadrupole Ordering and Rattling Motion of Clathrate Compound Pr3Pd20Ge6

“…Recently, it has been clarified that no sign of ultrasonic dispersion due to rattling motion is found in the R 3 Pd 20 Si 6 (R ¼ La, Ce, Pr, Nd) systems. 8,9) Thus, the replacement of Si by Ge, constituting of the cage at the 4a site, leads to the appearance of ultrasonic dispersion in R 3 Pd 20 Ge 6 systems. Based on these results, we conclude that the ultrasonic dispersion is caused by the rattling motion at the 4a site.…”

“…The isostructural compounds Ce 3 Pd 20 Si 6 and Pr 3 Pd 20 Si 6 show the elastic softening of ðC 11 À C 12 Þ=2 and C 44 , and antiferroquadrupole (AFQ) ordering at low temperatures with anisotropic magnetic phase diagrams. 8,9) The transverse ultrasonic C 44 mode of Ce 3 Pd 20 Ge 6 and La 3 Pd 20 Ge 6 shows a characteristic frequency dependence around 20 K in the elastic constant C 44 and the attenuation coefficient 44 . 2,3) This ultrasonic dispersion is caused by a thermally activated rattling motion of the guest rare-earth ions at the 4a site.…”