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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Correa, V. F., D. Betancourth, J. G. Sereni, N. Caroca-Canales, and C. Geibel. "Remarkable magnetostructural coupling around the magnetic transition in CeCo0.85Fe0.15Si." Journal of Physics: Condensed Matter 28, no. 34 (2016): 346003.
Abstract: We report a detailed study of the magnetic properties of CeCo0.85Fe0.15Si under high magnetic
fields (up to 16 Tesla) measuring different physical properties such as specific heat, magnetization,
electrical resistivity, thermal expansion and magnetostriction. CeCo0.85Fe0.15Si becomes
antiferromagnetic at TN 6.7 K. However, a broad tail (onset at TX 13 K) in the specific heat
precedes that second order transition. This tail is also observed in the temperature derivative of
the resistivity. However, it is particularly noticeable in the thermal expansion coefficient where it
takes the form of a large bump centered at TX. A high magnetic field practically washes out that tail
in the resistivity. But surprisingly, the bump in the thermal expansion coefficient becomes a well
pronounced peak fully split from the magnetic transition at TN. Concurrently, the magnetoresistance
also switches from negative to positive above TN. The magnetostriction is considerable and
irreversible at low temperature ( (16 T) 4×10− L
L
4 at 2 K) when the magnetic interactions
dominate. A broad jump in the field dependence of the magnetostriction observed at low T may be
the signature of a weak ongoing metamagnetic transition. Taking altogether the results indicate the
importance of the lattice effects on the development of the magnetic order in these alloys.
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Correa, V. F., I. Curci, J. G. Sereni, N. Caroca Canales, and C. Geibel. "Magnetic-field-tuned valence susceptibility in CeCo1−xFexSi revealed by magnetostriction." In Journal of Physics: Conference Series, 012042. Vol. 2164., 2022.
Abstract: We report magnetoelastic studies in the CeCo1−xFexSi alloys. Iron doping has a profound effect on the low temperature linear magnetostriction. At T = 2 K, the strength of the magnetostriction peaks at x = 0.23 where it reaches a value as large as $\[\frac{{\Delta L}}{L} = 3 \times {10^{ – 3}}\]$ in an applied magnetic field B = 16 T. This Fe concentration corresponds to the critical one xc above which long-range antiferromagnetic order is no longer observed. The progressive increment of the hibridization between the Ce 4f orbital and the conduction band, as the magnetic order vanishes, gives rise to a sizeable valence susceptibility that can be finely tuned by the magnetic field explaining the large magnetostrictive effect around xc. At higher x, the magnetostriction decreases, in agreement with a weaker valence susceptibility resulting from a stronger hibridization.
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Custers, J., T. Cichorek, P. Gegenwart, N. Caroca-Canales, O. Stockert, C. Geibel, F. Steglich, P. Pedrazzini, and J. G. Sereni. "Non-Fermi liquid effects close to a QCP in CeIn3-xSnx." ACTA PHYSICA POLONICA B 34, no. 2 (2003): 379–382.
Abstract: Resistivity and specific heat measurements at low temperatures on CeIn3-xSnx samples with concentrations x = 0.6, 0.65 and 0.7 demonstrate that with increasing Sn-alloying, the antiferromagnetic ordering temperature decreases continuously down to T = 0 K and disappears at a quantum critical point. We observe non-Fermi liquid (NFL) behavior in the resistivity and the specific heat, however the temperature dependencies are different from the predictions for a spin density wave (SDW) scenario. The resistivity at the critical point shows e.g., a linear temperature dependence, as expected for two dimensional fluctuations, which however can be excluded in the cubic structure of CeIn3-xSnx.
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de la Cruz, M. E., J. G. Sereni, and H. Salva. Calibración de Termómetros en el rango de 4K a 40K. Buenos Aires, 1977.
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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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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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Fernandez, G. E., M. G. Berisso, O. Trovarelli, and J. G. Sereni. "Comparative study of the ferro-antiferromagnetic transition in Ce(Fe,Co)(2) and Ce(Fe,Al)(2)." Journal of Alloys and Compounds 261, no. 1-2 (1997): 26–31.
Abstract: The magnetic, thermal and transport properties of Ce(Fe,Co)(2) and Ce(Fe,Al)(2) around the ferro-antiferromagnetic (F-AF) transition are studied and compared in their thermodynamic aspects. We confirm the presence of a structural contribution to the enthalpy of the transition in the case of Co substitution, which is the main difference between the AF phase transitions in both systems. The role of the Ce hybridization in the Co case and the ''canted'' nature of the AF phase in Ce(Fe,Al)(2) are discussed. (C) 1997 Elsevier Science S.A.
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Fraga, G. L. F., D. E. Brandao, and J. G. Sereni. "Specific heat of X2MnSn (X = Co, Ni, Pd, Cu), X2MnIn (X = Ni, Pd) and Ni2MnSb Heusler compounds." Journal of Magnetism and Magnetic Materials 102, no. 1-2 (1991): 199–207.
Abstract: Results of low-temperature specific heat measurements (1.5-8.0 K) on X2MnSn (X = Co, Ni, Pd, Cu), X2Mnln (X = Ni, Pd) and Ni2MnSb Heusler compounds are presented. All the compounds, except the cobalt based one, exibit a lattice spectrum anomaly described by an Einstein's term (soft-phonons). For all but one compound, the experimental values of the electronic specific heat coefficients are, at least, twice as big as the theoretical estimates. For two compounds it was possible to determine the magnetic effective field on Mn nuclei.
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