Berger, S., R. Hauser, H. Michor, G. Hilscher, E. Bauer, J. G. Sereni, and P. Rogl. "Thermodynamic properties of Ce(RuxRh1-x)3B2." Physica B 259-261 (1999): 116–117.
Abstract: Investigations of the magnetic phase diagram of Ce(RuxRh1-x)(3)B-2 were complemented by detailed specific heat and susceptibility measurements revealing complex magnetic order without spontaneous magnetisation. This regime follows the ferromagnetic phase on Rh/Ru substitution for x greater than or similar to 0.06. (C) 1999 Elsevier Science B.V. All rights reserved.
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Berisso, M. G., P. Pedrazzini, M. Deppe, O. Trovarelli, C. Geibel, and J. G. Sereni. "Composition dependence of the magnetic properties of Ge-doped CeCu2Si2." PHYSICA B-CONDENSED MATTER 320, no. 1-4 (2002): 380–383.
Abstract: Due to the proximity of CeCu2Si2 to a quantum critical point, the ground state of this compound is extremely sensitive to sample preparation conditions. Small excess of one component can lead to magnetic or superconducting behaviors. We found that in the alloy CeCu2(Si1-xGex)(2) a small excess of Ge enhances the homogeneity range allowing a precise investigation of stoichiometric effects on the physical properties. In this system, Ge doping produces an increment of the antiferromagnetic transition temperature T-N, while the superconducting one decreases. Particularly, it was found that at x = 0.1 both phases coexist at low temperature. In order to investigate the stability of these phases against changes of the Ce-ligands composition, we prepared a series of CeCu2+y(Si0.9Ge0.1)2-x, samples (0less than or equal toyless than or equal to0.10) and investigated their specific heat and electrical resistivity. We observed that the substitution of Si/Ge by Cu increases the characteristic temperature and weakens the magnetic contribution without modifying TN. A further transition, of the first order character, is observed at lower temperature. (C) 2002 Elsevier Science B.V. All rights reserved.
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Berisso, M. G., P. Pedrazzini, J. G. Sereni, O. Trovarelli, C. Geibel, and F. Steglich. "Study of Ce(Rh1-xPdx)(2)Si-2: pronounced differences between the CeRh2Si2 and CePd2Si2 ground states." EUROPEAN PHYSICAL JOURNAL B 30, no. 3 (2002): 343–349.
Abstract: We present electrical resistivity and specific heat measurements of alloys on the Rh rich side of the phase diagram of the Ce(Rh1-xPdx)(2)Si-2 system. We compare these results with those obtained at intermediate and low Rh concentrations. The analysis of the concentration and temperature dependence of the entropy and of the scaling behaviour of C-et(T) and rho(T) clearly confirm a separation of the magnetic phase diagram into two regions: the region x less than or equal to 0.3, showing a concentration independent characteristic temperature for the 4f-electrons with T-0 approximate to 45 K, while for x > 0.3, T-0 decreases to T-0(x = 1) approximate to 15 K. At low Pd-content, T-N decreases very rapidly from T-N = 36 K in pure CeRh2Si2 to T-N = 18 K at x = 0.1. With higher Pd concentration T-N stabilizes at T-N approximate to 15 K whereas the magnitude of the anomalies in C-et(T) and in the susceptibility around T-N are further reduced and disappear at x approximate to 0.3. This differs from the behavior found on the Pd-rich side, where T-N decreases continuously to zero with increasing Rh content. The pronounced differences observed between both phase boundaries and the drastic effect of doping on the Rh rich side suggest an itinerant character in CeRh2 Si-2, in contrast with the localized character of CePd2Si2. Further evidence for the itinerant character of CeRh2Si2 is given by the rho(T) dependence observed for x less than or equal to 0.3, which scales with rho(T) of the prototype itinerant compound YCo2.
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Berisso, M. G., O. Trovarelli, P. Pedrazzini, G. Zwicknagl, C. Geibel, F. Steglich, and J. G. Sereni. "Nonmonotonous evolution of the Kondo temperature in the phase diagram of Ce(Pd1-xCux)(2)Si-2." Physical Review B – Condensed Matter and Materials Physics 58, no. 1 (1998): 314–321.
Abstract: The evolution of the behavior of the Ce 4f electron with the Cu content in the alloy Ce(Pd1-xCux)(2)Si-2 was investigated by determining its structural, magnetic, transport, and thermal properties. Results obtained on 15 samples with compositions distributed along the whole concentration range allow us to draw a magnetic phase diagram showing three distinct regions. The first region at low Cu concentrations corresponds to the antiferromagnetic-ordered regime. The fast suppression of this magnetic order between x = 0.2 and x = 0.25 suggests the presence of a critical point which separates this region from the second one at larger.x values where no magnetic order is observed. The main characteristic of this second region, which extends up to x = 0.7, is a pronounced increase of the Kondo temperature T-K, from T-K approximate to 15 K at x = 0.25 to T-K approximate to 50 K at x = 0.7. This is in contrast with the fast decrease of T-K in the region with x > 0.7. In this region a small anomaly with a ferromagnetic character is observed in the specific hear arround 4 K. The change in the evolution of T-K with x coincides with a change in the composition dependence of the c lattice parameter of the tetragonal structure, pointing to a structure-related origin of this unusual T-K(x) behavior. This nonmonotonous T-K(x) dependence is reproduced using local-density-approximation band-structure calculations, which show a maximum of the hybridization strength between conduction electrons and Ce 4f stares for intermediate Cu concentrations. Such a T-K(x) dependence which contradicts the monotonous dependence observed in all other Ce-based alloy systems is the hallmark of the Ce(Pd1-xCux)(2)Si-2 alloy, which cannot be described as a Fermi-Liquid system in the nonmagnetic region. [S0163-1829(98)02118-3].
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Besnus, M. J., J. P. Kappler, M. F. Ravet, A. Meyer, R. Lahiouel, J. Pierre, E. Siaud, G. L. Nieva, and J. G. Sereni. "Structural and magnetic properties of the ternary rare earth (RE) compound series REInAu2(RE~La to Lu, Y)." Journal of the less-common metals 120, no. 1 (1986): 101–112.
Abstract: Results of structural, magnetic and heat capacity studies are reported for the REInAu2 series (except europium). A crystallographic transformation from cubic to tetragonal structure occurs for the compounds with lanthanum, cerium, praseodymium and neodymium. With the exception of LaInAu2, the phase transition has no observable effect on the magnetic susceptibility. Compounds formed with gadolinium, terbium, dysprosium and holmium order antiferromagnetically at low temperature. In this series YbInAu2 is confirmed to be in an unstable valence state with the maximum 2J + 1 = 8 ground state degeneracy.
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Braghta, A., G. Schmerber, A. Derory, J. G. Sereni, and J. P. Kappler. "Magnetic and thermal properties of Ce2Pd2Sn." Journal of Magnetism and Magnetic Materials 320, no. 6 (2008): 1141–1145.
Abstract: X-ray diffraction, susceptibility and specific heat studies on ternary Ce2Pd2Sn intermetallic compound and on its isostructural nonmagnetic compound La2Pd2Sn are reported. On Ce2Pd2Sn in absence of magnetic field, we confirm the existence of two magnetic transitions at T-N = 4.8K (antiferromagnetic transition) and T-C = 2.2K (ferromagnetic transition) and the specific heat results, measured down to 0.5 K, allow to recognize the transition at 2.2K as a first-order transition. A description based on molecular field calculations for the S = 1/2 resonant level model leads to a characteristic Kondo T-K of about 3K. (C) 2007 Elsevier B.V. All rights reserved.
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Braun, E., A. Bürger, G. L. Nieva, B. Roden, and J. G. Sereni. "Unexpected magnetic behaviour in a singlet crystal field ground state induced by Tb 4f-instability." Zeitschrift für Physik B Condensed Matter 70, no. 2 (1988): 187–192.
Abstract: The magnetic susceptibility (chi) of Th1-x Tb x alloys (with 5<x<55a/o Tb) in the range of 1 K<T<350K and the specific heat (forx=1.5a/o Tb) for 0.5<T<10 K were measured. A maximum in chi(T) was observed at a temperature which depends on concentration. The crystal field level scheme that fits the specific heat measurements shows two non-magnetic singlets as lowest levels. Such ambiguity is discussed within the framework of the 4f-Tb instability. The results are in agreement with the matrix superconductiveT c decrease. The contribution of the interconfigurational mixing on chi and the specific heat is also discussed.
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Braun, E., A. Bürger, B. Roden, and J. G. Sereni. "Spin glass-like behaviour of the singlet ground state system: ThTb." Solid State Communications 66, no. 11 (1988): 1141–1144.
Abstract: We have studied the temperature and field dependence of the magnetic susceptibility, X, on the single-ground-state Th1?nTbn system, in the 0.2 < n < 0.6 concentration range. The characteristic maximum of a spin glass transition was found at a temperature Tg, which increases linearly with the impurity concentration. As expected, the maximum of X is reduced by the increment of the applied magnetic field. The spin glass order parameter, as well as its critical exponent were evaluated by using the Sherrington-Kirkpatrick theory.
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Braun, E., G. Jackel, B. Roden, J. G. Sereni, and D. Wohlleben. "Comparative study of the specific heat of superconducting and non-superconducting YBa2Cu3O7-x." Zeitschrift für Physik B Condensed Matter 72, no. 2 (1988): 169–173.
Abstract: We have measured the specific heat, the electrical resistance and the magnetic susceptibility of YBa2Cu3O7−x in a superconducting (sc) and in a non-superconducting (nsc) version. The latter was obtained by inducing a small loss of oxygen. In the sc sample we find a jump of the specific heat with ΔC=3.6 J mole−1 K−1. Below the maximum nearT c the specific heat of the sc version drops too fast for an electronic effect alone: there is a cross-over from excess to deficiency already at 0.9T c . The specific heat of the nsc version shows a change of slope in the temperature range between 70 and 80 K, which indicates the existence of a second specific heat anomaly, which apparently exists independently of that due to the onset of superconductivity and explains at least partially the premature crossover.
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Carreras Oropesa, W. G., V. F. Correa, J. G. Sereni, D. J. García, and P. S. Cornaglia. "Landau theory for magnetic and structural transitions in CeCo0.85Fe0.15Si." Journal of Physics: Condensed Matter 30 (2018): 295803.
Abstract: We present a phenomenological analysis of the magnetoelastic properties of CeCo0.85Fe0.15Si
at temperatures close to the Néel transition temperature TN. Using a Landau functional we
provide a qualitative description of the thermal expansion, magnetostriction, magnetization
and specific heat data. We show that the available experimental results (Correa et al 2016 J.
Phys.: Condens. Matter 28 346003) are consistent with the presence of a structural transition
at Ts TN and a strong magnetoelastic coupling. The magnetoelastic coupling presents a
Janus-faced effect: while the structural transition is shifted to higher temperatures as the
magnetic field is increased, the resulting striction at low temperatures decreases. The strong
magnetoelastic coupling and the proximity of the structural transition to the onset temperature
for magnetic fluctuations, suggest that the transition could be an analogue of the tetragonal to
orthorhombic observed in Fe-based pcnictides.
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