|Ultrasonic investigation of field-dependent ordered phases in the filled skutterudite compound PrOs4As12
T. Yanagisawa, W. M. Yuhasz, T. A. Sayles, P. -C. Ho, M. B. Maple, H. Watanabe, Y. Yasumoto, Y. Nemoto, T. Goto, Z. Henkie and A. Pietraszko
Elastic constant measurements down to 0.48 K and in magnetic fields up to 11 T were performed on a single crystal of the filled skutterudite compound PrOs4As12. The longitudinal CL111=CB+4C44/3 mode shows Curie-type softening below ~25 K, which is explained in terms of the quadrupole susceptibility modified by a crystalline electric field with a Γ4(2) ground state. A detailed H-T phase diagram for H ||  is compiled with the elastic anomalies, which appear on the boundaries of two ordered phases at temperatures below 2.3 K and in fields below 3 T. The intermediate phase between 2 and 2.5 T assumes the aspect of antiferroquadrupolar ordering.
Figure : Magnetic field vs. Temperature (H-T) phase diagram of PrOs4As12 with fields (a) H ||  and (b) H || [1-10]. Data points are determined by a feature of elastic anomalies; upward or downward in CL111 vs. H (solid circles and squares), CL111 vs. T (open circles and squares); minimum in CL111 vs. H (times), CL111 vs. T (plus). Error bars on the markers indicate roughly estimated transition width. Solid lines are guides to the eyes, separating the PM region (phase I), AFM region (phase III) and unknown ordered phase II and II'.(*This research was performed at Niigata University in 2007-2008.)