Weak coupling magnetism in Ce₄Pt₁₂Sn₂₅: a small exchange limit in the Doniach phase diagram

Abstract

Magnetic susceptibility, magnetization, specific heat, and electrical resistivity studies on single crystals of Ce 4 Pt 12 Sn 25 reveal an antiferromagnetic transition at T N = 0.19 K, which develops from a paramagnetic state with a very large specific heat coefficient (C/T ) of 14 J mol −1 K −2 -Ce just above T N . On the basis of its crystal structure and these measurements, we argue that a weak magnetic exchange interaction in Ce 4 Pt 12 Sn 25 is responsible for its low ordering temperature and a negligible Kondo-derived contribution to physical properties above T N . The anomalous enhancement of specific heat above T N is suggested to be related, in part, to weak geometric frustration of f -moments in this compound.

Thermal and magnetic properties of the low-temperature antiferromagnetCe4Pt12Sn25

“…As expected, there is a large discrepancy at T = 0.2 K between experimental results and the calculated field dependence based on a single-ion CEF model so that only the saturated magnetic moment s = 0.74 B / Ce is comparable to the experimental value ͑ s = 0.71 B / Ce͒. The best fit to the data at 0.2 K below 0.4 T using a Kondo screening model 34 gives T K = 1.2 K. However, this value of T K is incompatible with specific-heat results and the analysis performed above, which indicate T K Յ 0.2 K. 25 At intermediate fields the dominant physics is in the f-f interactions inherent in the Heisenberg model that we used to describe specificheat results above. The magnetization calculated for T = 0.1 and 0.2 K is also displayed in Fig.…”

“…We assume that the ground state is a ⌫ 7 doublet. B 4 0 = 0.5 K then corresponds to the CEF splitting between ⌫ 7 and the first excited state ⌬ Ϸ 200 K, which can be inferred from S mag ͑T͒ and resistivity data, 25 respectively. As shown in the inset of Fig.…”

“…The details of the sample growth and the physical properties are described in Ref. 25. Specific heat was measured in a SHE dilution refrigerator with 9 T superconducting magnet by means of a quasiadiabatic heat-pulse method with a RuO 2 thermometer.…”

“…Large U-U distance d U-U ϳ 6 Å in UM 2 Zn 20 ͑M =Co,Rh͒ family of materials reduces the overlap between the 5f-electron wave functions, allowing for observation of sharp crystal electric fields ͑CEFs͒, a situation very rare in U compounds. 23 At the same time, this U-U separation resulted in a good description of the system within a Kondo 25 Previous specific-heat, resistivity, and ac-susceptibility measurements uncovered a phase transition at 0.18 K. 25 However, the origin of the transition was not identified. In this paper, we report the low-temperature specific-heat ͑C͒ and magnetization ͑M͒ measurements in magnetic field.…”

Thermal and magnetic properties of a low-temperature antiferromagnet Ce4Pt12Sn25

“…Recently, we succeeded in growing single crystals of Ce 4 Pt 12 Sn 25 with relatively large physical dimensions ͑up to ϳ5 ϫ 5 ϫ 5 mm 3 ͒. 25 Previous specific-heat, resistivity, and ac-susceptibility measurements uncovered a phase transition at 0.18 K. 25 However, the origin of the transition was not identified. In this paper, we report the low-temperature specific-heat ͑C͒ and magnetization ͑M͒ measurements in magnetic field.…”