Magnetism and heavy fermion-like behavior in the RBiPt series

Abstract

Members of the RBiPt (R =Ce-Lu with the exceptions of Pm and Eu) series have been grown as single crystals. Magnetic susceptibility and electrical resistance have been measured on all members of the series, and specific heat measurements have been performed on rcprcscntatives. Tue high temperature resistance uniformly changes from that of a small-gap semiconductor or semimetal seen in NdBiPt to that of a heavy-fermion meta! seen in YbBiPt, which shows a linear coefficient of specific heat at low temperatures of 8 J/K. 2 mole.Further, the lighter rare earth members s how an unusually sharp increase in their resistance associated with antiferromagnetic ordering at low temperatures.

Groundstate properties of YbBiPt

“…l(a) is intrinsic to YbBiPt. The resistive anomaly seen in YbBiPt at 0.45 K is qualitatively similar to those seen in other members of the RBiPt series [2]. Figure 3 There currently seem to be three possible origins of the resistive anomaly that accompanies the transition to the antiferromagnetic groundstate: (i) localized moments order and a superzone gap emerges as a result of the magnetically imposed periodicity, (ii) a spin density wave (SDW) forms out of the conduction band, also leading to a partial gapping of the Fermi surface, or (iii) there is a cooperative Jahn-Teller effect accompanying the magnetic order of localized moments that leads to a distortion of the lattice to tetragonal or lower symmetry.…”

“…origin [3,7,9] and has a magnetic susceptibility consistent with antiferromagnetism [1,2,6]. In addition, the size of the ordered moment detected by ~SR measurements is 0.1p.…”

“…The discovery of a linear contribution to the low-temperature specific heat in excess of 8 J/ mol K 2 in YbBiPt [1] has caused great interest in this last magnetic member of the RBiPt series [2] (R --rare earth). Although a substantial body of data from diverse measurements has formed [3][4][5][6][7][8][9], a unified picture of the groundstate has not emerged.…”

High-resolution x-ray diffraction study of the heavy-fermion compound YbBiPt

“…1,5 A sample approximately 1.5 mm thick with smooth surfaces was chosen for the measurements, and excess flux was carefully removed from the surfaces prior to the experiments. High-energy x-ray diffraction measurements were made at station 6-ID-D at the Advanced Photon Source using an x-ray wavelength of λ = 0.09407Å and a beam size of 60 × 60 µm.…”

“…YbBiPt is a heavy-fermion compound which manifests an extraordinary Sommerfeld coefficient of ≈ 8 J/mol-K 2 and spin-density-wave type antiferromagnetic (AFM) order below a Néel temperature of T N = 0.4 K. [1][2][3][4][5][6] The low value of T N reflects the fact that the dominant magnetic energy scales are all small and comparable -the Kondo temperature T K ≈ 1 K, 2 the Weiss temperature θ W ≈ −2 K, 5 and the crystallineelectric-field (CEF) splitting is on the order of 1 -10 K. 7 As a consequence, the compound's electronic states are very responsive to small applied magnetic fields and pressures, 5,8 and recent neutron diffraction measurements have shown that the AFM order is quite fragile. 6 The magnetic phase diagram indicates that, as T → 0 K, AFM order persists up to a critical applied magnetic field of µ 0 H c ≈ 0.4 T, followed by a region of non-Fermi liquid behavior up to ≈ 0.8 T, above which Fermi-liquid behavior occurs up to at least 6 T. 5 It has been proposed that a magnetic-field-induced quantum-critical point occurs at µ 0 H c .…”