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Trovarelli, O., P. Stickar, J. G. Sereni, G. Schmerber, and J. P. Kappler. "Coexistence of magnetic and non magnetic states in Ce14X51 (X = Au, Ag and Cu)." Solid State Communications 89, no. 5 (1994): 421–424.
Abstract: Magnetic (chi), thermal(C-p), and transport (p) measurements on Ce(l4)X(51) (X = Au, Ag and Cu) are presented. All these compounds show antiferromagnetic type order at low temperatures, with T-N = 0.9 K (Au), 1.1 K (Ag) and 3.2 K (Cu). Within the Gd14Ag51-type structure the Ce atoms sit in different sublattices denoted by I (2 atoms), II (6 atoms) and III (6 atoms), therefore the results can be interpreted in terms of three different behaviors of Ce depending on its local environment. From the entropy involved in the magnetically ordered (MO) phase it can be established that the Ce-II and Ce-III atoms order in Cel4Au51 and Ce14Ag51, while the Ce-I order in Cel4Cu51. There is a large linear contribution to Cp at T > T-N,T-gamma HT = 0.81 (Au), 1.24 (Ag) and 3.1 (Cu) J/mol K-2, which indicates the coexistence of MO and heavy fermions. In the case of Cel4Cu51, the magnetic contribution to Cp from sublattice Ce-I around T-N,T- resembles that of a modulated system and the characteristic temperatures for Ce-II and Ce-III atoms are estimated from p(T) as:T-K=16 K and >120 K respectively.
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TROVARELLI, O., J. G. SERENI, G. SCHMERBER, and J. P. KAPPLER. "COEXISTENCE OF KONDO AND SPIN-GLASS BEHAVIOR IN CE4Y3NI3." JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 140 (1995): 1211–1212.
Abstract: Magnetic susceptibility chi and specific heat C-p measurements on Ce4Y3Ni3 are presented. The temperature of the maximum of chi(ac)(T) and C-p(T) shifts with frequency and applied field respectively, as expected for a spin glass (SG) system. The C-p (T --> 0) dependence corresponds to that of an anisotropic SG. According to the entropy gain two Ce atoms are involved in the SG contribution and two exhibit Kondo effect.
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TROVARELLI, O., J. G. SERENI, G. SCHMERBER, and J. P. KAPPLER. "Low-temperature magnetic and thermal properties of CePdSb." Physical Review B – Condensed Matter and Materials Physics 49, no. 21 (1994): 15179–15183.
Abstract: Low-temperature ac and dc magnetic susceptibility, high-field magnetization, and specific-heat measurements have been carried out on CePdSb. The magnetic measurements confirm the ferromagnetic transition at T(C) = 17 K as previously reported. However, no anomaly in the specific heat is observed at that temperature, but only the onset of the magnetic contribution, C(M)(T). The maximum of C(M)(T) is observed at T(max) = 9.7 K. The lack of a C(M)(T) jump at T(C) is discussed in terms of the comparison of the exchange integrals between first- and second-nearest magnetic neighbors. Depending on their relative values, the magnetic structure can behave as low dimensional or incommensurate. The entropy of the magnetic phase (Rln2) and the low density of states (gamma = 11 mJ/mol K2) excludes a Kondo-lattice character for this compound.
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Sereni, J. G., O. Trovarelli, G. Schmerber, and J. P. Kappler. "Non-Fermi-liquid signatures in stoichiometric Ce7Ru3 at ambient pressure." Physica B – Condensed Matter 259-261 (1999): 405–406.
Abstract: Magnetic (chi(-1) proportional to root T) and thermal (C-p/T proportional to – log T) temperature dependencies of stoichiometric Ce7Ru3 are studied in order to establish whether its low temperature behavior corresponds to that of a non-Fermi-liquid system at normal pressure. Despite its reduced unit cell volume this compound shows a broadened antiferromagnetic transition, which involves only a small fraction of the expected entropy at T = T-n = 0.8 K. Scaling properties of C-p/t = -A log(t) + ETo (with t = T/T-o) under magnetic field (B) are fulfilled with A = 7.2 J and E = 0.07 B. The thermal characteristics of the transition itself are compared with those of other Ce compounds that also exhibit a “Lambda-shape” in the C-p/T(T) dependence around T-n. (C) 1999 Elsevier Science B.V. All rights reserved.
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Sereni, J. G., O. Trovarelli, G. Schmerber, and J. P. Kappler. "Comparative study of thermal and magnetic properties of CeTyX4-y ferromagnets." Physical Review B – Condensed Matter and Materials Physics 56, no. 9 (1997): 5380–5386.
Abstract: Low-temperature thermal (specific heat, C-P) and magnetic [ac susceptibility, chi(ac), and isothermal magnetization M(B)] measurements on CeTyX4-y ferromagnets (with T = Ni, Cu, Pd, Ag, Au, and X = Ga, Al, with 0.3 < y < 0.7) are reported. With the exception of T = Ni, all compounds with X = Ga show a typical second-order ferromagnetic transition. In the case of T = Ni, magnetic correlations set in at T approximate to 3T(C), (T-C being the Curie temperature) and the C-P(T) and chi(ac)(T) maxima (at 3.3 and 4.2 K, respectively) do not coincide, while the M(B) curves reveal an antiferromagnetic character at lower temperatures. In these systems, the magnetic entropy of the ordered phase is larger than 85% of Rln2, in coincidence with the low values of the Sommerfeld coefficient gamma less than or equal to 10 mJ/mol K-2. For T = Ag and X = Al, a strong diamagnetic signal was observed at T-s = 0.63 K in chi(ac)(T), with the characteristics of a superconducting component. The thermodynamical properties of these compounds confirm the lack of hybridization when the Ce atom is in a ferromagnetic ground state.
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Sereni, J. G., O. Trovarelli, G. Schmerber, and J. P. Kappler. "Coexistence of magnetic order and heavy fermion behavior in Ce7X3." Journal of Magnetism and Magnetic Materials 108, no. 1-3 (1992): 183–184.
Abstract: Low temperature specific heat and magnetic susceptibility measurements on Ce7X3 (X = Rh, Ni) compounds are reported. Ce7Rh3 shows an onset of spontaneous magnetization at 7.2 K. About 40% of the expected R ln 2 entropy gain is found in the paramagnetic phase, related to a gamma(HT) = 1.1 J/K2 mol specific heat coefficient. In Ce7Ni3 an antiferromagnetic transition is observed at 1.7 K, superimposed to a large C(p)/T electronic contribution, described by a gamma(HT) = 0.9 J/K2 mol coefficient for T > 10 K. These results are interpreted in terms of the three different crystal sublattices of Ce. The entropy gain related to each transition allows to identify the behaviour of each sublattice. In the case of Ce7Ni3 one sublattice behaves as a heavy fermion system, with a value of C(p)/T = 3.3 J/K2 Ce at. Such a behaviour is confirmed under an applied magnetic field.
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Sereni, J. G., O. Trovarelli, J. Schaf, G. Schmerber, and J. P. Kappler. "Extremely Low Density of States in CePd7." Modern Physics Letters B 5, no. 18 (1991): 1249–1253.
Abstract: The low temperature specific heat and magnetic susceptibility measurements, up to room temperature, on CePd7 are reported. The Sommefeld coefficient gamma and the Pauli susceptibility chio were found to have the lowest values within the Ce compounds: gamma = 9.8 mJ/mole K2 and chio = 0.14 × 10-3 emu/mole. The ratio chio/gamma = 0.014 emu K2/J is that of a free electron, instead of an intermediate valence system (0.036 emu K2/J). Such a value suggests complete delocalization of the Ce 4f electrons.
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Sereni, J. G., G. Schmerber, and J. P. Kappler. "Thermodynamic Behavior of Ce Compounds Close to a T->0 Critical Point." IEEE Transactions on Magnetics 49, no. 8 (2013): 4647–4651.
Abstract: There is a reduced group of Ce very heavy Fermions (VHF) which do not order magnetically down to at least T ≈ 500 mK because they are very close to a Tord = 0 critical point. These compounds are at the top of the limT→ 0 Cm/T specific heat values because they collect very high density of low energy excitations. From the analysis of Cm(T)/T and entropy Sm(T) dependencies performed on selected CePd3Mx ternaries (where M = B and Be) a quantitative evaluation of an upper limit for the density of excitations can be proposed. These observations exclude any evidence of Cm(T)/T divergency as T→ 0 in agreement with thermodynamic laws. A comparison with selected Yb-base VHF supports these features.
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Sereni, J. G., G. Schmerber, M. G. Berisso, B. Chevalier, and J. P. Kappler. "Tricritical point and suppression of the Shastry-Sutherland phase in Ce2(Pd1−xNix)2Sn." Physical Review B – Condensed Matter and Materials Physics 85, no. 13 (2012): 134404.
Abstract: Structural, magnetization, and heat capacity measurements were performed on Ce2(Pd1−xNix)2Sn compounds covering the full range of the Mo2FeB2 structure stability (0⩽x⩽0.25). In this system, the two transitions observed in Ce2Pd2Sn (antiferromagnetic TN=4.8 K and ferromagnetic TC=2.1 K) converge into a tricritical point at Tcr≈3.4 K for xcr≈0.3, where the intermediate antiferromagnetic (AF) phase is suppressed. The decrease of the TN(x) phase boundary is due to an incipient Kondo screening of the Ce-4f moments. This effect and the increase of local atomic disorder affect the formation of Ce-magnetic dimers on which the Shastry-Sutherland lattice (SSL) builds up. On the contrary, the TC(x) transition to the ferromagnetic ground state increases as a consequence of the weakening of the intermediate phase. Applied magnetic fields also suppress the AF-SSL phase as it was already observed in the stoichiometric compound.
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Sereni, J. G., M. Gómez Berisso, G. Schmerber, and J. P. Kappler. "Suppression of the Shastry-Sutherland phase in Ce2 Pd 2 Sn at a field-induced critical point." Physical Review B – Condensed Matter and Materials Physics 81, no. 18 (2010): 184429.
Abstract: The magnetic phase diagram of Ce2 Pd2 Sn is investigated through the field dependence of thermal, transport, and magnetic properties at low temperature. The upper transition, TM =4.8 K is slightly affected by magnetic field up to B=1 T whereas the lower one T C (B) rapidly increases from 2.1 K joining TM in a critical point at Tcr = (4.1±0.2) K for Bcr = (0.11±0.01) T. At that point, the intermediate phase, previously described as an unstable Shastry-Sutherland lattice, is suppressed. A detailed analysis around the critical point reveals a structure in the maximum of the ∂ M/∂ B (B) derivative, which may be related to a step in magnetization predicted by theory for the mentioned lattice. © 2010 The American Physical Society.
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