GERENCIA DE ÁREA INVESTIGACIÓN, DESARROLLO E INNOVACIÓN (GAIDI)
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Ítem Acceso Abierto CeRuGe and CeRuSi: Heavy fermion systems with some unusual features(IOP Publishing, 2010-00-00) Sereni, J.G.; Caroca-Canales, N.; Kumar, M.; Oeschler, N.; Gómez Berisso, M.; Geibel, C.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasWe have investigated the physical properties of CeRuSi, its homologue CeRuGe and some doped La alloys. All of them present similar properties: large paramagnetic temperatures θp ≈ −100 K and the level off of χ(T) below ≈ 10 K in coincidence with the maximum decrease of p(T), which starts to drop below 25 K. The respective γ(CeRuSi) ≊ 0.18 and γ(CeRuGe) ≊ 0.15 J/molK2 coefficients reveal a heavy fermion character, with a Kondo temperature TK ≊ 50 K comparable to the crystal field splitting. In both compounds a broad maximum in CP(T)/T is observed around 5 K, whose origin is yet not clear. In contrast to the usual behavior observed in Kondo lattice systems, when Si is replaced by Ge TK ∝ θp and 1/γ practically does not decreases despite the unit cell volume of CeRuGe is about 3% larger than that of CeRuSi. We discuss possible origins for these unusual features.Ítem Acceso Abierto Evidence of spin-density-wave to spin-glass transformation in YNd alloys(American Physical Society, 1995-12-01) Trovarelli, O.; Sereni, J.G.; Pureur, P.; Shaf, J.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasLow-temperature ac and dc magnetic susceptibility and specific-heat measurements have been carried out on YNd dilute alloys, where the Nd concentrations are 1.9, 2.5, 4.5, 6.8, and 9.0 at. %. The most concentrated alloys (4.5, 6.8, and 9.0 at. %) present long-range antiferromagnetic spin-density-wave (SDW) order below the critical temperature, but some residual frustration is likely to produce a reentrant behavior at low temperatures, where the magnetic data show strong irreversibility effects and the specific heat indicates the occurrence of an anisotropy induced gap near zero frequency in the density of states of the magnetic excitations. For the less concentrated alloys (1.9 and 2.5 at. %), the interacting magnetic state shows typical features of spin-glass behavior. The evolution to this state is ascribed as being due to impurity disorder and frustration which induces a breaking up of the SDW coherence into small domains.Ítem Acceso Abierto Experimental study of physical properties in the complex magnetic phase diagram of Ce(Rh1-xRux)(3)B-2(American Physical Society, 2001-00-00) Berger, S.; Galatanu, A.; Hilscher, G.; Michor, H.; Paul, C.; Bauer, E.; Rogl, P.; Gomez-Berisso, M.; Pedrazzini, P.; Sereni, J.G.; Kappler, J.P.; Rogalev, A.; Matar, S.; Weill, F.; Chevalier, B.; Etourneau, J.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasWe report on a series of structural, magnetic, and thermodynamic measurements, a study of transport properties and x-ray absorption edge spectroscopy on Ce(Rh1−xRux)3B2. These investigations evidence that in addition to the already established ferromagnetic range for x<~0.06, a complex antiferromagnetic structure exists for concentrations 0.1<~x<~0.35. The behavior in the latter regime is dominated by an extraordinary strong intersite coupling; however, the magnetic moments involved appear to be very small. At the phase boundary to the paramagnetic regime (x≈0.4), significant deviations from a Fermi-liquid behavior occur.Ítem Acceso Abierto First order magnetic transition and magnetoelastic effects in Sm2IrIn8(Elsevier, 2008-04-01) Lora-Serrano, R.; Correa, V. F.; Adriano,C.; Giles, C.; Duque, J.G.S.; Granado, E.; Pagliuso, P.G.; Murphy, T.P.; Palm, E.C.; Tozer, S.W.; Lacerda, A.H.; Sarrao, J.L.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasWe report measurements of temperature dependent heat capacity, thermal expansion and high resolution X-ray diffraction (XRD) taken on single crystals of Sm2IrIn8 intermetallic compound. This compound belongs to the RmMnIn3mþ2n family (R = rare earth, m = 1, 2, n = 0, 1 and M = Rh, Ir and Co) which includes a number of heavy fermion superconductors for R = Ce. Particularly, Sm2IrIn8 is the only member of this family to present a first order magnetic phase transition (FOMT). Both thermal expansion and heat capacity data show very pronounced sharps peaks at TN = 14.2 K consistent with an FOMT. The linear thermal-expansion coefficient is anisotropic and both c-axis and basal ab plane coefficients change discontinuously at 14.2 K. This change is negative for both direction in contrast to what was found for other members of family such as Ce 2 RhIn8 and CeRhIn 5. The zero-field high resolution XRD data at 14.2 K shows no evidence for a tetragonal-to-orthorhombic structural phase transition. We discuss our results considering tetragonal crystalline field effects (CEF), quadupolar interactions, antiferromagnetic domains and magnetoelastic effects.Ítem Acceso Abierto Gradual pressure-induced enhancement of magnon excitations in CeCoSi(American Physical Society, 2020-06-00) Nikitin, S.E.; Franco, D.G.; Kwon, J.; Bewley, R.; Podlesnyak, A.; Hoser, A.; Koza, M.M.; Geibel, C.; Stockert, O.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasCeCoSi is an intermetallic antiferromagnet with a very unusual temperature-pressure phase diagram: at ambient pressure it orders below TN=8.8K, while application of hydrostatic pressure induces a new magnetically ordered phase with exceptionally high transition temperature of ∼40K at 1.5 GPa. We studied the magnetic properties and the pressure-induced magnetic phase of CeCoSi by means of elastic and inelastic neutron scattering (INS) and heat capacity measurements. At ambient pressure CeCoSi orders into a simple commensurate AFM structure with a reduced ordered moment of only mCe=0.37(6)μB. Specific heat and low-energy INS indicate a significant gap in the low-energy magnon excitation spectrum in the antiferromagnetic phase, with the CEF excitations located above 10 meV. Hydrostatic pressure gradually shifts the energy of the magnon band towards higher energies and the temperature dependence of the magnons measured at 1.5 GPa is consistent with the phase diagram. Moreover, the CEF excitations are also drastically modified under pressure.Ítem Acceso Abierto Low Temperature magnetic properties of GdCoIn5(Elsevier, 2015-01-15) Betancourth, D.; Facio, J.I.; Pedrazzini, P.; Jesus, C.B.R.; Pagliuso, P.G.; Vildosola, V.; Cornaglia, P.S.; García, D. J.; Correa, V. F.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasA comprehensive experimental and theoretical study of the low temperature properties of GdCoIn5 was performed. Specific heat, thermal expansion, magnetization and electrical resistivity were measured in good quality single crystals down to 4He temperatures. All the experiments show a second-order-like phase transition at 30 K probably associated with the onset of antiferromagnetic order. The magnetic susceptibility shows a pronounced anisotropy below TN with an easy magnetic axis perpendicular to the crystallographic ĉ-axis. Total energy GGA+U calculations indicate a ground state with magnetic moments localized at the Gd ions and allowed a determination of the Gd-Gd magnetic interactions. Band structure calculations of the electron and phonon contributions to the specific heat together with Quantum Monte Carlo calculations of the magnetic contributions show a very good agreement with the experimental data. Comparison between experiment and calculations suggests a significant anharmonic contribution to the specific heat at high temperature (T≳100 K).Ítem Acceso Abierto Low temperature thermopower and magnetoresistance of Sc-rich CeSc1-xTixGe(Elsevier, 2018-05-01) Encina, S.; Pedrazzini, P.; Sereni, J.G.; Geibel, C.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasIn CeSc 1-xTixGe, Ti-alloying reduces the record-high antiferromagnetic (AFM) ordering temperature found in CeScGe at T = 46 KN 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 ρ 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 f4 and band states. This is a further hint pointing to the local character of magnetism in this alloy. Magnetic fields up to 16 T have a minor effect on the electrical resistivity of stoichiometric CeScGe. On the other hand, for x = 0.65, we find that fields above 4 T suppress the hump in ρ T( ). Furthermore, the 4.2 K magnetoresistance displays a strong decrease in the same field range, also in coincidence with magnetization results from the literature. Our results indicate that ρ T H( , ) is a proper tool to assess the H T− phase diagram of this system.Ítem Acceso Abierto Magnetic properties of SrTiO3/Pr2/3Ca 1/3MnO3 multilayers(IOP Publishing, 2010-00-00) Niebieskikwiat, D.; Haberkorn, N.; Guitarra, R.; Guimpel, J.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasNanoscale ferromagnetic (FM) clusters embedded within insulating (I) layers of the antiferromagnetic Pr2/3Ca1/3MnO3 (PCMO) are known to improve the magnetoresistance ratio of FM-I magnetoresistive multilayers. Here, we study the magnetic properties of perovskite superlattices comprised of five PCMO layers of variable thickness t separated by 5nm-thick spacers of SrTiO3 (STO). Several multilayers (1.5 nm ≤ t ≤ 8 nm) were grown on (001) STO substrates by magnetron sputtering. We show that the magnetic moment of PCMO due to the FM inclusions presents a maximum for t ~ 3 nm, accompanied by an abrupt increase of coercivity and exchange bias field. The nonmagnetic nature of the neighboring STO layers demonstrates that the observed behavior is not related to any interlayer exchange coupling, but the geometrical matching between layer thickness and FM domain size is the key driver for the enhancement of the FM moment and anisotropy energy. These results open a new door for the optimization of perovskite based spintronic devices.Ítem Acceso Abierto Magnetic properties of the Ce-Rh binary phases(EDP Sciences, 1988-12-00) Kappler, J.P.; Lehmann, P.; Schmerber, G.; Nieva, G.; Sereni, J.G.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasCrystallographic, magnetic and resistivity studies on the Ce-Rh binary phases clearly define two Ce ground state regions : i) CeRh3, CeRh2 and CeRh as intermediate valence compounds and ii) Ce5Rh4, Ce3Rh2 Ce5Rh3 and Ce7Rh3 with magnetic transitions at low temperature.Ítem Acceso Abierto Nonmonotonous evolution of the Kondo temperature in the phase diagram of Ce(Pd1-xCux)(2)Si-2(American Physical Society, 1998-07-01) Berisso, M.G.; Trovarelli, O.; Pedrazzini, P.; Zwicknagl, G.; Geibel, C.; Steglich, F.; Sereni, J.G.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasThe evolution of the behavior of the Ce 4f electron with the Cu content in the alloy Ce(Pd1−xCux)2Si2 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 TK, from TK≈15 K at x=0.25 to TK≈50 K at x=0.7. This is in contrast with the fast decrease of TK in the region with x>0.7. In this region a small anomaly with a ferromagnetic character is observed in the specific heat arround 4 K. The change in the evolution of TK 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 TK(x) behavior. This nonmonotonous TK(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 states for intermediate Cu concentrations. Such a TK(x) dependence which contradicts the monotonous dependence observed in all other Ce-based alloy systems is the hallmark of the Ce(Pd1−xCux)2Si2 alloy, which cannot be described as a Fermi-liquid system in the nonmagnetic region.Ítem Acceso Abierto Quantum criticality in the cubic heavy-fermion system CeIn3-xSnx(American Physical Society, 2006-06-25) Kuchler, R.; Gegenwart, P.; Custers, J.; Stockert, O.; Caroca-Canales, N.; Geibel, C.; Sereni, J.G.; Steglich, F.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasWe report a comprehensive study of CeIn3−xSnx (0.55≤x≤0.8) single crystals close to the antiferromagnetic quantum-critical point (QCP) at xc≈0.67 by means of the low-temperature thermal expansion and Grüneisen parameter. This system represents the first example for a cubic heavy fermion in which TN can be suppressed continuously down to T=0. A characteristic sign change of the Grüneisen parameter between the antiferromagnetic and paramagnetic states indicates the accumulation of entropy close to the QCP. The observed quantum-critical behavior is compatible with the predictions of the itinerant theory for three-dimensional critical spin fluctuations. This has important implications for the role of the dimensionality in heavy-fermion QCPs.Ítem Acceso Abierto Specific heat of CeIn3-xSnx single crystals in the vicinity of the quantum critical point(Elsevier, 2005-04-30) Rus, T.; Wilhelm, H.; Stockert, O.; Luhmann, T.; Caroca-Canales, N.; Sereni, J.G.; Geibel, C.; Steglich, F.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasWe report on results of low-temperature specific heat experiments on single crystals of the cubic alloy CeIn 3-xSnx (x = 0:55; 0:60; 0:65; and 0.80). The measurements support three-dimensional critical spin fluctuations in the vicinity of the magnetic instability, i.e. for xc ≈ 0:67; where the antiferromagnetic order vanishes.Ítem Acceso Abierto The magnetic instability of Yb2Pd2(In,Sn) in a non-Fermi liquid environment(IOP Publishing, 2005-03-04) Bauer, E.; Hilscher, G.; Michor, H.; Paul, Ch.; Aoki, Y.; Sato, H.; Adroja, D.T.; Park, J.-G.; Bonville, P.; Godart, C.; Sereni, J.G.; Giovannini, M.; Saccone, A.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasVarious concentrations of the solid solution Yb2Pd2In1−xSnx ranging from x = 0 to 1 with the tetragonal Mo2FeB2-type structure were prepared and their physical properties were studied by means of bulk and spectroscopic measurements as a function of temperature, pressure and magnetic fields. Results deduced from these studies indicate a slight variation of the valency of the Yb ions, from for both border compounds to ν = 3 at x = 0.6. This variation gives rise to the appearance of long range magnetic order in a narrow concentration region around x = 0.6, while both border compounds remain non-magnetic. The outstanding concentration dependence for the ordered regime may be indicative of two quantum critical points, a novel feature not yet observed in Yb compounds.Ítem Acceso Abierto Tricritical point and suppression of the Shastry-Sutherland phase in Ce2(Pd1−xNix)2Sn(American Physical Society, 2012-04-02) Sereni, J.G.; Schmerber, G.; Berisso, M.G.; Chevalier, B.; Kappler, J.P.; Gerencia Física. Departamento Materia Condensada. División Bajas TemperaturasStructural, 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.