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Author (up) Betancourth, D.; Correa, V. F.; Facio, J.I.; Fernández J.; Vildosola, V.; Lora-Serrano, R.; Cadogan, J.M.; Aligia, A.A.; Cornaglia, P.S.; García D.J.
Title Magnetostriction reveals orthorhombic distortion in tetragonal Gd compounds Type Journal Article
Year 2019 Publication Physical Review B Abbreviated Journal Phys. Rev. B
Volume 99 Issue Pages 134406
Keywords
Abstract We report detailed thermal expansion and magnetostriction experiments on GdCoIn5 and GdRh(In1−xCdx )5

(x = 0 and 0.025) single-crystal samples that show a sudden change in the dilation at a field B for temperatures

below the Néel transition temperature TN . We present a first-principles model including crystal-field effects,

dipolar and exchange interactions, and the dependence of the latter with lattice distortions in order to fully

account for the magnetostriction and magnetic susceptibility data. The mean-field solution of the model shows

that a transition between metastable states occurs at the field B. It also indicates that two degenerate phases

should coexist at temperatures below TN , which may explain the lack of observation, in high-resolution

x-ray experiments, of an orthorhombic distortion at the Néel transition, even though the experimentally

determined magnetic structure breaks the tetragonal symmetry and the magnetoelastic coupling from our model

is significant. These conclusions could be extended to other tetragonal Gd-based compounds that present the

same phenomenology.
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Call Number BT @ victor.correa @ Serial 815
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Author (up) 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.
Title Low Temperature magnetic properties of GdCoIn5 Type Journal Article
Year 2015 Publication Journal of Magnetism and Magnetic Materials Abbreviated Journal J. Magn. Magn. Mater.
Volume 374 Issue Pages 744-747
Keywords
Abstract A 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 T N 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 (View the MathML sourceT≳100K).
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Call Number BT @ victor.correa @ Serial 701
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Author (up) Correa, V. F., P. Pedrazzini, D. G. Franco, A. J. Rosa, B. Rubrecht, N. Haberkorn
Title Low-temperature thermal expansion of the topological material candidates β-PtBi2 and β-PdBi2 Type Journal Article
Year 2022 Publication Physica B – Condensed Matter Abbreviated Journal Physica B
Volume 641 Issue Pages 414102
Keywords
Abstract We report on the low-temperature ($T <$ 120 K) thermal expansion of the bismuth-based topological semimetal $\beta$-PtBi$2$ and topological superconductor $\beta$-PdBi$2$ candidates.

The linear thermal-expansion coefficient of tetragonal $\beta$-PdBi$2$ shows a pronounced anisotropy between the $a$- and $c$-axis while the volume thermal-expansion coefficient $\alphaV$($\beta$-PdBi$2$) is considerable larger than $\alphaV$($\beta$-PtBi$2$).

The coefficient $\alpha
V$($\beta$-PtBi$2$) nearly matches the experimental specific heat, from which a Debye temperature $\thetaD =$ 199 K is obtained. On the other hand, $\alphaV$($\beta$-PdBi$2$) reasonably fits the Debye model with $\thetaD =$ 138 K, extracted from the low-temperature specific heat.

An almost constant Gr\"uneisen parameter $\Gamma \approx$ 2 is obtained for both compounds.

No magnetostriction is observed in any of both compounds up to $\mu
0 H =$ 16 T.

We compare our results with other Bi-based topological materials.
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Call Number BT @ victor.correa @ Serial 882
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Author (up) Correa, V. F.; Castro, F. J.
Title First-Order Phase Transformation at Constant Volume: A Continuous Transition? Type Journal Article
Year 2022 Publication Entropy Abbreviated Journal Entropy
Volume 24 Issue Pages 31
Keywords
Abstract We describe a first-order phase transition of a simple system in a process where the

volume is kept constant. We show that, unlike what happens when the pressure is constant, (i) the

transformation extends over a finite temperature (and pressure) range, (ii) each and every extensive

potential (internal energy U, enthalpy H, Helmholtz energy F, and Gibbs energy G), and the entropy

S is continuous across the transition, and (iii) the constant-volume heat capacity does not diverge

during the transition and only exhibits discrete jumps. These non-intuitive results highlight the

importance of controlling the correct variables in order to distinguish between continuous and

discontinuous transitions. We apply our results to describe the transition between ice VI and liquid

water using thermodynamic information available in the literature and also to show that a firstorder

phase transition driven in isochoric condition can be used as the operating principle of a

mechanical actuator.
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Call Number BT @ victor.correa @ Serial 879
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Author (up) Correa, V. F; Villagrán Asiares, A. G.; Betancourth, D.; Encina, S.; Pedrazzini, P.; Cornaglia, P.S.; García D.J.; Sereni, J. G.; Maiorov, B; Caroca-Canales, N; Geibel, Ch.
Title Strong magnetoelastic effect in CeCo1−xFexSi as Néel order is suppressed Type Journal Article
Year 2019 Publication Physical Review B Abbreviated Journal Phys. Rev. B
Volume 100 Issue Pages 184409
Keywords
Abstract A very strong magnetoelastic effect in the CeCo1−xFexSi alloys is reported. The strength of the magnetostrictive

effect can be tuned upon changing x. The moderate low-temperature linear magnetostriction observed at low

Fe concentrations becomes very large (L

L (16T, 2K) = 3 × 10−3) around the critical concentration xc ≈ 0.23 at

which the long-range antiferromagnetic order vanishes. Upon increasing doping through the nonmagnetic region

(x > xc), the magnetostriction strength gradually weakens again. The interplay between magnetic order and the

Kondo screening appears to cause an enhanced valence susceptibility slightly changing the Ce ions valence,

ultimately triggering the large magnetostriction observed around the critical concentration. Previous studies

of the evolution of the lattice parameters with x as well as magnetization and x-ray absorption spectroscopy

measurements support this hypothesis.
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Call Number BT @ victor.correa @ Serial 842
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Author (up) Facio, J.I.; Betancourth, D.; Pedrazzini, P.; Correa, V. F; Vildosola, V.; García, D. J.; Cornaglia, P.S.
Title Why the Co-based 115 compounds are different: The case study of GdMIn5 (M = Co,Rh,Ir) Type Journal Article
Year 2015 Publication Physical Review B Abbreviated Journal Phys. Rev. B
Volume 91 Issue Pages 014409
Keywords
Abstract The discovery in 2001 of superconductivity in some heavy fermion compounds of the RMIn5 (R = 4f or

5f elements; M = Co, Rh, Ir) family, has triggered an enormous amount of research into understanding the

physical origin of superconductivity and its relation with magnetism. Although many properties have been

clarified, there are still crucial questions that remain unanswered. One of these questions is the particular role

of the transition metal in determining the value of critical superconducting temperature (TC). In this work, we

analyze an interesting regularity that is experimentally observed in this family of compounds, where the lowest

N´eel temperatures are obtained in the Co-based materials. We focus our analysis on the GdMIn5 compounds

and perform density-functional-theory-based total-energy calculations to obtain the parameters for the exchange

coupling interactions between the magnetic moments located at the Gd3+ ions. Our calculations indicate that

the ground state of the three compounds is a C-type antiferromagnet determined by the competition between

the first- and second-neighbor exchange couplings inside GdIn3 planes and stabilized by the couplings across

MIn2 planes. We then solve a model with these magnetic interactions using a mean-field approximation and

quantum Monte Carlo simulations. The results obtained for the calculated N´eel and Curie-Weiss temperatures,

the specific heat, and the magnetic susceptibility are in very good agreement with the existent experimental data.

Remarkably, we show that the first-neighbor interplane exchange coupling in the Co-based material is much

smaller than in the Rh and Ir analogs which leads to a more two-dimensional magnetic behavior in the former.

This result explains the observed lower N´eel temperature in Co-115 systems and may shed light on the fact that

the Co-based 115 superconductors present the highest TC.
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Notes Approved no
Call Number BT @ victor.correa @ Serial 705
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Author (up) 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.
Title First order magnetic transition and magnetoelastic effects in Sm2IrIn8 Type Journal Article
Year 2008 Publication Physica B Abbreviated Journal
Volume 403 Issue 5-9 Pages 1365-1367
Keywords First order magnetic phase transition; Magnetotrictive effects; CEF effects
Abstract We 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 RmMnIn3m+2n 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 View the MathML source 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 Ce2RhIn8 and CeRhIn5. 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.
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Area Expedition Conference International Conference on Strongly Correlated Electron Systems
Notes Approved no
Call Number BT @ hernan @ Serial 307
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