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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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Deppe, M., N. Caroca-Canales, J. G. Sereni, and C. Geibel. "Evidence for a metamagnetic transition in the heavy Fermion system CeTiGe." In Journal of Physics: Conference Series, 012026. Vol. 200. International Conference on Magnetism, ICM 2009 200, no. SECTION 1. Karlsruhe, 2010.
Abstract: A recent study of CeTiGe identified this compound as a paramagnetic heavy Fermion system where the full J = 5/2 multiplet is involved in the formation of the ground state. Here we present a preliminary investigation of the dc-magnetization Mdc(H) and of the magnetoresistance Ï(H) of polycrystalline CeTiGe samples in applied magnetic fields up to μ0H = 14 T. The results reveal a pronounced metamagnetic transition at a critical field μ0Hc ≈ 13.5 T at low temperatures, with a step like increase in Mdc(H) of at least 0.6 μB/Ce. The metamagnetic transition leads to a strong decrease in Ï(H). A clear hysteresis in Mdc(H) and Ï(H) indicate that in CeTiGe these metamagnetic features correspond to a true thermodynamic, first order type transition in contrast to the critical behavior observed in the canonical system CeRu2Si2. Measurements at higher temperatures showed a continuous suppression of the metamagnetic transition with increasing T, which vanishes at T ∼ 30 K. © 2010 IOP Publishing Ltd.
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Deppe, M., P. Pedrazzini, N. Caroca-Canales, C. Gelbel, and J. G. Sereni. "Investigations of CePd1-xRhx single crystals located near a ferromagnetic quantum critical point." PHYSICA B-CONDENSED MATTER 378-380 (2006): 96–97.
Abstract: Investigations of CePd1-xRhx polycrystals have revealed a continuous transition from a ferromagnetic state at x = 0 to an intermediate valence state at x = 1 and evidenced non-Fermi liquid behavior near the critical concentration x(c) approximate to 0.85 where T-C is continuously suppressed to T = 0 K. We present here first results of specific heat and magnetization measurements on CePd1-xRhx single crystals with composition close to the critical point. They confirm the results obtained on polycrystals and reveal a rather low magnetic anisotropy, despite the orthorhombic structure. (c) 2006 Elsevier B.V. All rights reserved.
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Hartmann, S., M. Deppe, N. Oeschler, N. Caroca-Canales, J. G. Sereni, and C. Geibel. "Ferromagnetism in CePd1-xRhx single crystals." Journal of Optoelectronics and Advanced Materials 10, no. 7 (2008): 1607–1611.
Abstract: The orthorhombic CePd1-xRhx alloy exhibits a continuous evolution from a ferromagnetic ground state at x = 0 to
intermediate-valence behavior for x = 1. Here, we report on specific heat CP(T), resistivity Ï(T) and magnetization M(T)
measurements on single crystals in a Rh concentration range 0.2 < x < 0.65 exploring the ferromagnetic side of the
magnetic phase diagram. The transport and thermodynamic properties of the ferromagnetic phase have been investigated
in the temperature range from 300 K down to 0.35 K and analyzed in terms of a gap in the magnon spectrum and an
underlying Kondo contribution. Crystal electric field parameters are deduced from specific heat measurements well above
Tc- The competition between Kondo effect and ferromagnetism has been studied in dependence of the Rh concentration in
the system. Particularly, the enhanced Sommerfeld coefficient γ(x) indicates strong Kondo interactions when the Curie
temperature is reduced.
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Pedrazzini, P., M. G. Berisso, N. Caroca-Canales, M. Deppe, C. Geibel, and J. G. Sereni. "Low temperature magnetic phase diagram of the cubic non-Fermi liquid system Celn(3-x)Sn(x)." The European Physical Journal B – Condensed Matter 38, no. 3 (2004): 445–450.
Abstract: In this paper we report a comprehensive study of the magnetic susceptibility (x), resistivity (p), and specific heat (C-P), down to 0.5 K of the cubic CeIn3-xSnx alloy. The ground state of this system evolves from antiferromagnetic (AF) in CeIn3 (T-N = 10.2 K) to intermediate-valent in CeSn3, and represents the first example of a Ce-lattice cubic non-Fermi liquid (NFL) system where T-N(x) can be traced down to T = 0 over more than a decade of temperature. Our results indicate that the disappearance of the AF state occurs near x(c) approximate to 0.7, although already at x approximate to 0.4 significant modifications of the magnetic ground state are observed. Between these concentrations, clear NFL signatures are observed, such as rho(T) approximate to rho(0) + A T-n (with n < 1.5) and C-P(T) proportional to -T ln(T) dependencies. Within the ordered phase a first order phase transition occurs for 0.25 < x < 0.5. With larger Sn doping, different weak rho(T) dependencies are observed at low temperatures between x = 1 and x = 3 while C-P/T shows only a weak temperature dependence.
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Pedrazzini, P., M. G. Berisso, N. Caroca-Canales, M. Deppe, C. Geibel, and J. G. Sereni. "Non-Fermi liquid behaviour in cubic CeIn3-xSnx." PHYSICA B-CONDENSED MATTER 312 (2002): 406–407.
Abstract: The alloy between the antiferromagnetic (AF) CeIn3 and the mixed valent CeSn3 is particularly interesting since it is one of the few cases where a magnetic to non-magnetic transition is observed in a cubic system. Although the resulting alloy CeIn3-xSnx has been investigated for over 20 years, no information is available about thermodynamic and transport properties below 2K. We report first measurements on resistivity rho(T) and specific heat C-P(T) down to 0.45 K. These results confirm the disappearance of the AF state near xcongruent to0.6. In samples close to this critical concentration, we observe a strong departure from the Fermi liquid behaviour, i.e. rho(T) approximate to rho(0) + a T-n (n < 1.5) and a logarithmic temperature dependence C-P(T)infinity – T ln (T), in more than a decade above the lowest investigated temperature. (C) 2002 Elsevier Science B.V. All rights reserved.
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Pedrazzini, P., M. G. Berisso, J. G. Sereni, N. Caroca-Canales, M. Deppe, and C. Geibel. "Complex magnetic phase diagram near the quantum critical point in CeIn3-xSnx." ACTA PHYSICA POLONICA B 34, no. 2 (2003): 363–366.
Abstract: A recent reinvestigation of the alloy system CeIn3-xSnx between the antiferromagnetic (AF) Kondo-lattice CeIn3 and the intermediate valent CeSn3 has shown that the AF order disappears at a quantum critical point (QCP) at x(c) approximate to 0.65. Preliminary evidences for a first order transition below T-N at x < x(c), indicating a complex magnetic phase diagram, have motivated the present detailed investigation of specific heat and resistivity on fine tuned samples in the 0.25 less than or equal to x less than or equal to x(c) range. These results confirm the first order transition at T-I < T-N in a reduced concentration range (0.25 < x < 0.47) and suggest that the phase boundary T-I (x) merge with the T-N(x) near x approximate to 0.37, leading to a tetracritical point. A similar first order transition was previously observed in the CeCu2(Si,Ge)(2) system at low Ge-concentration. Since in this alloy the first order transition also appears in the vicinity of a QCP, the question arises concerning how general this property is at AF critical points in Ce-based alloy systems.
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Pedrazzini, P., D. Jaccard, M. Deppe, C. Geibel, and J. G. Sereni. "Multiprobe high-pressure experiments in CePd0.6Rh0.4 and CePd3." Physica B: Condensed Matter 404, no. 19 (2009): 2898–2903.
Abstract: Results of recent multiprobe high-pressure experiments on ferromagnetic CePd0.6Rh0.4 and intermediate-valent CePd3 are presented. Simultaneous resistivity (ρ), thermopower (S), and ac heat capacity measurements show that the long-range ferromagnetic state of CePd0.6Rh0.4 vanishes in the proximity of a sharp valence-crossover pressure , i.e. before reaching a quantum critical point. However, a magnetic signal that is progressively suppressed is still detected at higher pressures. For CePd3, the results of simultaneous ρ(T,p) and S(T,p) measurements up to and down to the mK temperature range show a surprisingly weak pressure dependence.
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Pikul, A. P., N. Caroca-Canales, M. Deppe, P. Gegenwart, J. G. Sereni, C. Geibel, and F. Steglich. "Non-Fermi-liquid behaviour close to the disappearance of ferromagnetism in CePd1-xRhx." Journal of Physics: Condensed Matter 18, no. 42 (2006): L535–L542.
Abstract: The orthorhombic CePd1- xRhx system exhibits a continuous evolution from ferromagnetic order in CePd ( T-C = 6.6 K) to an intermediate-valence ground state in CeRh. Here we report low-temperature ( T >= 0.08 K) specific-heat measurements for concentrations 0.80 <= x <= 0.95 close to the disappearance of magnetic order (similar to 0.87). In contrast to x = 0.8, still demonstrating a smeared phase transition signature at 0.27 K, non-Fermi-liquid behaviour Delta C(T) / T alpha log T is observed in the electronic specific-heat coefficient at x = 0.85. For higher Rh concentrations a weak power-law dependence Delta C(T) / T alpha T-alpha with alpha approximate to 0.4 is found. Upon applying magnetic fields Fermi-liquid-like behaviour Delta C(T) / T similar to const is recovered in all the different samples. The magnetic entropy as well as the concentration of unscreened magnetic moments at 2 K indicate a broad distribution of local T-K values ranging from well below 2 K to far above 50 K.
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Sereni, J. G., M. Gomez Berisso, N. C. Canales, M. Deppe, and C. Geibel. "Tuning ground state degeneracy and quantum criticality in Ce1-xLaxTiGe." Physica Status Solidi (B) Basic Research 247, no. 3 (2010): 707–709.
Abstract: We have tuned the paramagnetic heavy Fermion (HF) system CeTiGe to a more magnetic state and toward quantum criticality (QC) by partially substituting La for Ce. The induced volume expansion leads to a pronounced decrease of the Kondo temperature (TK), from ≈50 K in pure CeTiGe to less than 4 K at large La content. Since the former value is of the order of the crystal field splitting, while the latter is well below, the systems evolves from a large degeneracy N = 6 Kondo system at x = 0 to a conventional N = 2 Kondo system at x ≥ 0:8. There, the first excited crystal field doublets become apparent in the T dependence of the specific heat CP(T) at an excitation energy DCF ≈ 30 K. The reduction of the degeneracy is expected to enhance the decrease of TK, explaining the strong reduction by more than one order of magnitude observed in this system. The decrease of TK drives the system toward QC as evidenced by a divergence of CP(T)/T and x(T) toward low temperatures in the x = 0:8 sample. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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