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Author Sereni, J.G.
Title Thermodynamic analysis of the quantum critical behavior of Ce-lattice compounds Type Journal Article
Year 2013 Publication Philosophical Magazine Abbreviated Journal Philos. Mag.
Volume 93 Issue 4 Pages 409-433
Keywords quantum criticality, entropy, magnetic phase diagrams
Abstract A systematic analysis of low-temperature magnetic phase diagrams of Ce compounds is performed in order to recognize the thermodynamic conditions to be fulfilled by those systems to reach a quantum critical regime or, alternatively, to identify other kinds of low-temperature behavior. Based on specific heat (C m ) and entropy results, three different types of phase diagrams are recognized: (i) with the entropy involved in the ordered phase (S MO) decreasing proportionally to the ordering temperature (T MO); (ii) those showing a transference of degrees of freedom from the ordered phase to a non-magnetic component, with their C m (T MO) jumps (ΔC m ) vanishing at finite temperature; and (iii) those ending at a critical point at finite temperature because their ΔC m do not decrease sufficiently with T MO, producing an entropy accumulation at low temperature. Only those systems belonging to the first case, i.e. with S MO → 0 as T MO → 0, can be regarded as candidates for quantum critical behavior. Their magnetic phase boundaries deviate from the classical negative curvature below T ≈ 2.5 K, denouncing monotonic misleading extrapolations down to T = 0. Different characteristic concentrations are recognized and analyzed for Ce-ligand alloyed systems. In particular, a pre-critical region is identified where the nature of the magnetic transition undergoes significant modifications, with its ∂C m /∂T discontinuity strongly affected by the magnetic field and showing an increasing remnant entropy at T → 0. Physical constraints arising from the third law at T → 0 are discussed and recognized from experimental results.
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Notes Approved no
Call Number BT @ pedrazp @ Serial 665
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Author Sereni, J.G.
Title Entropy Bottlenecks at T->0 in Ce-Lattice and Related Compounds Type Journal Article
Year 2015 Publication Journal of Low Temperature Physics Abbreviated Journal J. Low Temp. Phys.
Volume 179 Issue 1-2 Pages 126-137
Keywords Heavy fermions; Specific heat anomalies; Entropy
Abstract A number of specific heat Cm anomalies are reported in Ce- and Yb-lattice compounds around 1 K which cannot be associated to usual phase transitions despite of their robust magnetic moments. Instead of a Cm(T) jump, these anomalies show coincident morphology: (i) a significant tail in Cm/T , with similar power law decay above their maxima ( T>Tm ), (ii) whereas a Cm(T2) dependence is observed below Tm . (iii) The comparison of their respective entropy gain Sm(T) indicates that ≈0.7R ln2 is condensed within the T>Tm tail, in coincidence with an exemplary spin-ice compound. Such amount of entropy arises from a significant increase of the density of low energy excitations, reflected in a divergent Cm(T>Tm)/T dependence. (iv) Many of their lattice structures present conditions for magnetic frustration. The origin of these anomalies can be attributed to an interplay between the divergent density of magnetic excitations at T→0 and the limited amount of degrees of freedom: Sm = R ln2 for a doublet-ground state. Due to this “entropy bottleneck,” the paramagnetic minimum of energy blurs out and the system slides into an alternative minimum through a continuous transition. A relevant observation in these very heavy fermion systems is the possible existence of an upper limit for Cm/TLimT→0 ≈7 J/mol K 2 observed in four Yb- and Pr-based compounds.
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Publisher Springer US Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0022-2291 ISBN Medium
Area Expedition Conference
Notes Approved no
Call Number BT @ pedrazp @ Serial 709
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Author Sereni, J.G.
Title Role of entropy in the ground state formation of frustrated systems Type Journal Article
Year 2018 Publication Physica B: Condensed Matter Abbreviated Journal Physica B
Volume 536 Issue Pages 397-400
Keywords Entropy; Frustrated systems; Nernst postulate
Abstract The absence of magnetic order in Rare Earth-based frustrated compounds allows to recognize the action of the third law of thermodynamics in the low temperature behavior of those systems. One of the most relevant findings is the appearance of a coincident specific heat Cm/T|T→0≈7J/molK2 ‘plateau’ in six Yb systems. This characteristic feature occurs after a systematic modification of the thermal trajectory of their entropies Sm(T) in the range of a few hundred milikelvin degrees. Such behavior is explained by the formation of an entropy-bottleneck imposed by the third law constraint (Sm|T→0≥0), that drives the system into alternative ground states. Based in these finding, three possible approaches to the Sm|T→0 limit observed in real systems are analyzed in terms of the ∂2Sm/∂T2 dependencies.
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Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0921-4526 ISBN Medium
Area Expedition Conference
Notes Approved no
Call Number BT @ pedrazp @ Serial 768
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Author Sereni, J.G.
Title Analysis of Entropy trajectories in very Heavy Fermions for Adiabatic Demagnetization Refrigeration at the T<1K range Type Journal Article
Year 2019 Publication Materials Today: Proceedings Abbreviated Journal XXIII Latin American Symposium on Solid State Physics (SLAFES XXIII), San Carlos de Bariloche, Argen
Volume 14 Issue Pages 67-71
Keywords Adiabatic refrigeration; Entropy; Very Heavy Fermions
Abstract With the aim to improve classical paramagnetic salts performances for adiabatic magnetization refrigeration processes, relevant thermodynamic parameters of recently discovered very heavy fermion Yb-based intermetallic compounds are investigated within the sub-Kelvin range of temperature. Focusing on fixed thermal points, required for e.g. photonic devices operating within the 100 mK range in orbital satellites, the nature of respective magnetic ground states are discussed together with the effect of an 'entropy bottleneck' imposed by the Nernst postulate the entropy S(T) trajectories. To gain insight into the main criteria for a proper choice of suitable materials for alternative applications, thermomagnetic S(T,B) trajectories and respective derivatives: δS/δT and δS/δB, are analyzed as key parameters for this magnetocaloric process and compared with those from the classical salt Cerium-Magnesium-Nitride (CMN).
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Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 2214-7853 ISBN Medium
Area Expedition Conference
Notes Approved no
Call Number BT @ pedrazp @ Serial 823
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Author Sereni, J.G.
Title Thermomagnetic properties of very heavy fermions suitable for adiabatic demagnetisation refrigeration at low temperature Type Journal Article
Year 2020 Publication Philosophical Magazine Abbreviated Journal Philos. Mag.
Volume 100 Issue 10 Pages 1211
Keywords Magnetic refrigeration; heavy fermions; entropy; frustration; specific heat
Abstract With the aim to improve the performance of classical paramagnetic salts for adiabatic refrigeration processes at the sub-Kelvin range, relevant thermodynamic parameters of some new Yb-based intermetallic compounds are analysed and compared. Two main applications are considered: (i) those requiring temperature fixed-points to be reached applying magnetic fields of moderate intensity for satellite applications, and (ii) those which can be used for controlled thermal drifts in laboratory applications. Different thermomagnetic trajectories of the entropy are identified depending on respective specific heat behaviours and the constraints imposed by the Nernst postulate at the sub-Kelvin range. Some simple relationships are proposed to compare the diverse magnetocaloric characteristics of different systems. This procedure allows to include the classical Cerium-Magnesium-Nitride (CMN) salt in that comparison.
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Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 1478-6435 ISBN Medium
Area Expedition Conference
Notes Special Issue in Honour of M. Brian Maple Approved no
Call Number BT @ pedrazp @ Serial 862
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Author Sereni, J.G.; Gomez Berisso, M.; Braghta, A.; Schmerber, G.; Kappler, J.P.
Title Unstable Shastry-Sutherland phase in Ce2Pd2Sn Type Journal Article
Year 2008 Publication Physical Review B – Condensed Matter and Materials Physics Abbreviated Journal Phys. Rev. B
Volume 80 Issue 2 Pages 022428
Keywords cerium alloys; crystal field interactions; entropy; ferromagnetic materials; frustration; magnetic anisotropy; magnetic hysteresis: magnetic transitions; palladium alloys; tin alloys
Abstract Thermal (CP) , magnetic ( M and χac ), and transport (ρ) measurements on Ce2Pd2Sn are reported. High-temperature properties are well described by the presence of two excited crystal-field levels at (65±5)K and (230±20)K , with negligible hybridization (Kondo) effects. According to literature, two transitions were observed at TM=4.8K and TC=2.1K , respectively. The upper transition cannot be considered as a standard antiferromagnetic because of frustration effects in a triangular network of Ce atoms and the positive sign of the paramagnetic temperature θPLT=4.4K . The nature of the intermediated phase is described accounting for the formation of ferromagnetic (F) Ce dimers disposed in a quasi-two-dimensional square lattice, resembling a Shastry-Sutherland pattern. According to hysteretic features in ρ(T) and χac(T) , the lower F transition is of first order, with CP(T<TC) revealing a gap of anisotropy Eg≈7K .
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Notes Approved no
Call Number BT @ pedrazp @ Serial 563
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Author Sereni, J.G.; Schmerber, G.; Kappler, J.P.
Title Thermodynamic Behavior of Ce Compounds Close to a T->0 Critical Point Type Journal Article
Year 2013 Publication IEEE Transactions on Magnetics Abbreviated Journal IEEE Trans. Magn.
Volume 49 Issue 8 Pages 4647-4651
Keywords cerium compounds; critical points; entropy; palladium compounds; specific heat; CePd3Bx; CePd3Bex; cerium compounds; critical point; entropy; specific heat; thermodynamic behavior; Compounds; Entropy; Heating; Saturation magnetization; Temperature dependence; Temperature measurement; Thermodynamics; Cerium; magnetic properties; thermodynamics
Abstract There is a reduced group of Ce very heavy Fermions (VHF) which do not order magnetically down to at least T ≈ 500 mK because they are very close to a Tord = 0 critical point. These compounds are at the top of the limT→ 0 Cm/T specific heat values because they collect very high density of low energy excitations. From the analysis of Cm(T)/T and entropy Sm(T) dependencies performed on selected CePd3Mx ternaries (where M = B and Be) a quantitative evaluation of an upper limit for the density of excitations can be proposed. These observations exclude any evidence of Cm(T)/T divergency as T→ 0 in agreement with thermodynamic laws. A comparison with selected Yb-base VHF supports these features.
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Corporate Author Thesis
Publisher Place of Publication Editor
Language Summary Language Original Title
Series Editor Series Title Abbreviated Series Title
Series Volume Series Issue Edition
ISSN 0018-9464 ISBN Medium
Area Expedition Conference
Notes Approved no
Call Number BT @ pedrazp @ Serial 664
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