Low-temperature magnetism in YbBiPt

Abstract

PHYSICAL REVIE% B UOLUME 46, NUMBER 5 Low-temperature magnetism AUGUST 1992-I in YbBiPt A. Amato Institut fiir Mittelenergiephysik der Eidgenossische Technische Hochschule Ziirich, CH-5232 Villigen PSI, Switzerland P. C. Canfield Los Alamos National Laboratory, Los Alamos, New Mexico 87545 R. Feyerherm der Eidgenossische Technische Hochschule CH-5232 Villigen PSI, Switzerland Institut fu rMit'telenergiephysik Ziirich, Z. Fisk Los Alamos National Laboratory, Los Alamos, New Mexico 87545 F. N. Gygax der Eidgenossische Technisch Hochschule CH-5232 Villigen PSI, Switzerland Institut fiir Mittelenergiephysik Ziirich, R. H. Heffner Los Alamos National Laboratory, Los Alamos, New Mexico 87545 D. E. MacLaughlin* Kamerlingh Onnes Laboratorium, University of Leiden, 2300 RA Leiden, The Netherlands H. R. Ott Laboratorium fu'r FestkorperphysikEidge, nossische Technische Hochschule Honggerberg, CH-8093 Ziirich, Switzerland A. Schenck Institut fiir Mittelenergiephysik der Eidgenossische Technische Hochschule CH-5232 Villigen PSI, Switzerland Ziirich, J. D. Thompson Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (Received 13 April 1992) Positive-muon (p ) spin-relaxation experiments have been carried out in a pressed-powder sample of the low-carrier-density heavy-electron and disordered system YbBiPt. Spatially inhomogeneous static Yb magnetism is observed below 5 K, with a strongly reduced Yb moment of -O. ling over -50% of the sample volume at T=0. 06 K. Substantial p+ spin-lattice relaxation, rarely observed in heavy-electron systems, suggests anomalously slow Yb spin fluctuations. Our data are reminiscent of p+ behavior in spin glasses, and raise the question of whether the large low-temperature specific heat in YbBiPt is due in part to low-lying magnetic excitations. The RBiPt (R =rare earth) series of ternary interme- tallic compounds exhibits a rather unique evolution from insulating to weak metallic behavior with increasing rare- earth atomic number. ' Among these materials YbBiPt is of particular interest. Measurements of the specific heat yield an cp is Aux-grown single crystals of this compound enormous Sommerfeld coefficient T=c~/T=8 Jmol K below 4 K, suggestive of an extremely massive itinerant-electron state. A low characteristic temperature is indicated by an entropy release of Rln2 between zero and l K. A cusp in the ac susceptibility at 0. 4 K indicates some sort of low-temperature magnetic phase which seems to coexist with the heavy-electron state. The specific heat of crushed powders of YbBiPt (Ref. 3) is nearly the same as in unstrained material above 0. 5 K, but below this temperature the cp/T ratio is reduced by ap- proximately 50% and there is no clear evidence for a mag- netic phase transition. These results indicate that YbBiPt is situated on the boundary between magnetic and heavy-electron behavior with respect to the Yb spin degrees of freedom. Questions are raised concerning (1) the stability of the Yb moment, (2) the nature of a heavy-electron state which can evolve from a low-carrier-density metal at high temperatures, and (3) the competition between Kondo singlet formation Yosida interactions. and Rudermann-Kittel-Kasuya- This paper presents the results of positive-muon spin ro- tation (p+SR) experiments which bear on the above @1992 The American Physical Society