Giriat, G., G. W. Scheerer, Z. Ren, P. Pedrazzini, G. Lapertot, and D. Jaccard. "A watchmaker’s precision at high-pressure reveals CeCu 2 Si 2 and CeAu 2 Si 2 p-T phase diagrams." In Journal of Physics: Conference Series, 032008. Vol. 950., 2017.
Abstract: Gaétan Giriat and Gernot Werner Scheerer and Zhi Ren and Pablo Pedrazzini and Gerard Lapertot and Didier Jaccard
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Sereni, J. G., P. Pedrazzini, M. Gómez Berisso, A. Chacoma, S. Encina, T. Gruner, N. Caroca-Canales, and C. Geibel. "Exploring high temperature magnetic order in CeTi 1- x Sc x Ge." In Journal of Physics: Conference Series, 012005. Vol. 592., 2015.
Abstract: We studied the magnetic, transport, and thermodynamic properties of the alloy CeTi 1- x Sc x Ge in order to shed some light into the origin of the exceptionally large antiferromagnetic (AFM) ordering temperature T N = 47 K in pure CeScGe. We observed a complex magnetic phase diagram, which present an interesting dichotomy: Despite strong changes in the nature of the ordered state, from ferromagnetic (FM) for x ≤ 0.55 to AFM for x > 0.55, the ordering temperature increases smoothly and continuously from T C = 7 K at x = 0.25 to T N = 47 K at x = 1. Within the AFM regime we observe a metamagnetic transition at a critical field increasing from H = 0 at x ≈ 0.55 to μ 0 * H ≈ 6 Tesla at x = 1. Furthermore a second transition appears at T L ≤ T N for x ≥ 0.65. In contrast to observations in CeRh 2 Si 2 or CeRh 3 B 2 , we found no evidence for a strong hybridization of the 4f electrons at large Sc contents. Therefore the exceptionally large T N of CeScGe could be attributed to the unusually strong RKKY interaction in this type of compounds.
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Encina, S., P. Pedrazzini, J. G. Sereni, and C. Geibel. "Low temperature thermopower and magnetoresistance of Sc-rich CeSc1-xTixGe." Physica B: Condensed Matter 536 (2018): 133–136.
Abstract: In CeSc1-xTixGe, Ti-alloying reduces the record-high antiferromagnetic (AFM) ordering temperature found in CeScGe at TN=46K and induces ferromagnetism for x≥0.5. In this work we focus on the AFM side, i.e. Sc-rich samples, and study their thermopower S(T) and magnetoresistance Ï(H,T). The measured S(T) is small in comparison with the thermopower of other Ce-systems and shows some features that are compatible with a weak hybridization between the 4f and band states. This is a further hint pointing to the local character of magnetism in this alloy. Magnetic fields up to 16T have a minor effect on the electrical resistivity of stoichiometric CeScGe. On the other hand, for x=0.65, we find that fields above 4T suppress the hump in Ï(T). Furthermore, the 4.2K magnetoresistance displays a strong decrease in the same field range, also in coincidence with magnetization results from the literature. Our results indicate that Ï(T,H) is a proper tool to assess the H−T phase diagram of this system.
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Fasano, Y., P. Szabó, J. KaÄmarÄík, Z. Pribulová, P. Pedrazzini, P. Samuely, and V. F. Correa. "Unconventional superconductivity in the strong-coupling limit for the heavy fermion system CeCoIn5." Physica B: Condensed Matter 536 (2018): 798–802.
Abstract: We present scanning tunneling spectroscopy measurements of the local quasiparticles' excitation spectra of the heavy fermion CeCoIn5 between 440mK and 3K in samples with a bulk Tc=2.25K. The spectral shape of our low-temperature tunneling data, quite textbook nodal-Δ conductance, allow us to confidently fit the spectra with a d-wave density of states considering also a shortening of quasiparticles' lifetime term Γ. The Δ(0) value obtained from the fits yields a BCS ratio 2Δ/kTc=7.73 suggesting that CeCoIn5 is an unconventional superconductor in the strong coupling limit. The fits also reveal that the height of coherence peaks in CeCoIn5 is reduced with respect to a pure BCS spectra and therefore the coupling of quasiparticles with spin excitations should play a relevant role. The tunneling conductance shows a depletion at energies smaller than Δ for temperatures larger than the bulk Tc, giving further support to the existence of a pseudogap phase that in our samples span up to T*∼1.2Tc. The phenomenological scaling of the pseudogap temperature observed in various families of cuprates, 2Δ/kT*∼4.3, is not fulfilled in our measurements. This suggests that in CeCoIn5 the strong magnetic fluctuations might conspire to close the local superconducting gap at a smaller pesudogap temperature-scale than in cuprates.
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Carreras Oropesa, W. G., S. Encina, P. Pedrazzini, V. F. Correa, J. G. Sereni, V. Vildosola, García D.J., and P. S. Cornaglia. "Minimal model for the magnetic phase diagram of CeTi1-xScxGe, GdFe1-xCoxSi, and related materials." Journal of Magnetism and Magnetic Materials 503 (2020): 166614.
Abstract: We present a theoretical analysis of the magnetic phase diagram of CeTi1-xScxGe and GdFe1-xCoxSi as a function
of the temperature and the Sc and Co concentration x, respectively. CeScGe and GdCoSi, as many other RTX
(R=rare earth, T=transition metal, X=p-block element) compounds, present a tetragonal crystal structure
where bilayers of R are separated by layers of T and X. While GdFeSi and CeTi0.75Sc0.25Ge are ferromagnetic,
CeScGe and GdCoSi order antiferromagnetically with the R 4f magnetic moments on the same bilayer aligned
ferromagnetically and magnetic moments in nearest neighbouring bilayers aligned antiferromagnetically. The
antiferromagnetic transition temperature TN decreases with decreasing concentration x in both compounds and
for low enough values of x the compounds show a ferromagnetic behavior. Based on these observations we
construct a simplified model Hamiltonian that we solve numerically for the specific heat and the magnetization.
We find a good qualitative agreement between the model and the experimental data. Our results show that the
main magnetic effect of the Sc→Ti and Co→Fe substitution in these compounds is consistent with a change in
the sign of the exchange coupling between magnetic moments in neighbouring bilayers. We expect a similar
phenomenology for other magnetic RTX compounds with the same type of crystal structure.
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Bridoux, G., P. Pedrazzini, F. de la Cruz, and G. Nieva. "Angular field dependence of the Nernst effect in Bi2Sr2CaCu2O8+delta." PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 460 (2007): 841–842.
Abstract: The anomalous Nernst effect in hole-doped cuprates has been interpreted in terms of the existence of a superconducting order parameter well above the transition temperature, T-c(H). In order to improve the understanding of this problem, we have measured the angular field dependence of the Nernst signal in Bi2Sr2CaCu2O8+delta single crystals. The experiment was done tilting the magnetic field with respect to the direction of the temperature gradient, above and below T,(H), with applied fields up to 16 T. We have found that all the curves are scaled on one curve against the reduced field Hcos theta at a fixed temperature. (c) 2007 Elsevier B.V. All rights reserved.
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Facio, J. I., D. Betancourth, N. R. Cejas Bolecek, G. A. Jorge, P. Pedrazzini, V. F. Correa, P. S. Cornaglia, V. Vildosola, and García D.J. "Lattice specific heat for the RMIn5 (R=Gd, La,Y; M=Co, Rh) compounds: Non-magnetic contribution subtraction." Journal of Magnetism and Magnetic Materials 407 (2016): 406–4011.
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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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Pedrazzini, P., and D. Jaccard. "The critical pressure of chromium." Physica B: Condensed Matter 403, no. 5-9 (2008): 1222–1224.
Abstract: We present first results of high-pressure resistivity measurements on pure chromium. Two pieces of evidence show that spin density wave magnetism is suppressed at a critical pressure pc?10GPa, namely, the evolution of the ordering temperature TN(p) and the rapid decrease of the residual resistivity close to pc. Our discussion profits from the comparison between pressurized-Cr and the Cr1-xVx alloy, for which a large amount of information on its electronic properties is available.
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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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