Physica B 186-188 (1993) 475-477 North-Holland PHYSICA[ Neutron scattering and specific heat experiments in CePt2Sn 2 J.-M. Mignot a, R. Kahn a, M.-J. Besnus b, J.-P. Kappler b and C. Godart c *Laboratoire Ldon Brillouin, CEA-CNRS, CE-Saclay, Gif sur Yvette, France blPCMS-GEMME, lnstitut de Physique, Strasbourg, France CCNRS, UPR209, Meudon, France Inelastic neutron scattering and specific heat experiments have been performed down to 1.5 K on the heavy electron antiferromagnet CePt2Sn 2. From the quasielastic linewidth F(T-->O), a Kondo temperature Tr of about 1 K (i.e. TK~ TN) is determined. The specific heat displays a Schottky-type crystal field anomaly at Tma X ~ 40 K and an additional term at lower temperatures, which is consistent with the above value of TK. |. Introduction Sn-based CeM2Sn 2 materials (M = transition metal) have larger unit cell volumes than their Si and Ge counterparts and are thus good candidates for studying the competition of RKKY and Kondo interactions by the chemical pressure effect over a broader range of lattice parameters. The heavy electron compound CePtaSn 2 exhibits both a low antiferromagnetic order- ing temperature (T N = 0.88 K) and a huge electronic specific heat coefficient (C/T(T= T~)=3.5J/mole K2), suggesting a rather low value of the Kondo temperature (TK= Tr~) [1]. In order to study the dynamics of magnetic fluctuations in this material, we have performed inelastic neutron scattering experi- ments down to 1.5 K. We also report specific-heat measurements between 14 and 80 K, from which a crystal field anomaly and a low-temperature Kondo term can be identified. 2. Experiments CePtaSn 2 (and LaPt2Sn2, as a reference) poly- crystalline samples were prepared by arc-melting of the constituents, La, Ce (99.9%), Pt (99.99%) and Sn (99.999%) on a water-cooled copper hearth in an argon atmosphere. X-ray powder diffraction experi- ments were carried out using an automatic (Philips PF1381) goniometer with Cu K, radiation. No anneal- ing was performed so as to retain the CaBeEGe: Correspondence to: J.-M. Mignot, LLB, CE-Saclay, F-91191 Gif sur Yvette, France. primitive tetragonal variety [2]. The samples were found to be single-phase by metallographic examina- tion. Microprobe analysis using Camebax showed that they were also homogeneous and had the expected 122 stoichiometry, except for a slight Pt deficiency (-2.5%) which was systematically observed in differ- ent batches. Inelastic neutron scattering measurements were per- formed on the time-of-flight (TOF) spectrometer Mibemol at the reactor Orphre in Saclay, with an incoming neutron energy of 1.94 meV (6.5 A) giving a resolution at zero energy transfer of 40~eV (HWHM). The 44 detectors covered the angular range 37°~<20~<137 ° (It21=0.6 to 1.8/~ ~). To im- prove statistics, and because the angle dependence of the spectra was weak (see below), the counts from 5-6 adjacent detectors were cumulated and ascribed to the average 20 of the group. Spectra were collected in the paramagnetic phase at 1.8, 8.5, 30, 60, 120 and 180 K. However, only the first four had sufficient statistics and will be considered in the following discussion. The specific-heat measurements (1.4-80K) were per- formed by the usual pulse method [5] on both CePt2Sn 2 and the nonmagnetic isostructural reference LaPt2Sn 2. 3. Results and discussion The various TOF spectra are well represented by the sum of an incoherent elastic line, fitted according to a vanadium standard, and a Lorentzian 'quasi- elastic' line centered at zero energy transfer. No size- able wave-vector dependence is observed even at the lowest temperature, indicating that intersite correla- 0921-4526/93/$06.00 ~) 1993 - Elsevier Science Publishers B.V. All rights reserved