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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. doi  openurl
  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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  Notes Approved no  
  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. url  doi
openurl 
  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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  Notes Approved no  
  Call Number BT @ victor.correa @ Serial 701  
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Author (up) Carreras Oropesa, W.G.; Encina, S.; Pedrazzini, P.; Correa, V.F.; Sereni, J.G.; Vildosola, V.; García D.J.; Cornaglia, P.S. doi  openurl
  Title Minimal model for the magnetic phase diagram of CeTi1-xScxGe, GdFe1-xCoxSi, and related materials Type Journal Article
  Year 2020 Publication Journal of Magnetism and Magnetic Materials Abbreviated Journal  
  Volume 503 Issue Pages 166614  
  Keywords Magnetism; RTX  
  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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  Notes Approved no  
  Call Number BT @ victor.correa @ Serial 856  
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Author (up) Facio, J.I.; Betancourth, D.; Cejas Bolecek, N.R.; Jorge, G.A.; Pedrazzini, P.; Correa, V.F.; Cornaglia, P.S.; Vildosola, V.; García D.J. url  doi
openurl 
  Title Lattice specific heat for the RMIn5 (R=Gd, La,Y; M=Co, Rh) compounds: Non-magnetic contribution subtraction Type Journal Article
  Year 2016 Publication Journal of Magnetism and Magnetic Materials Abbreviated Journal J. Magn. Magn. Mater.  
  Volume 407 Issue Pages 406-4011  
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  Notes Approved no  
  Call Number BT @ victor.correa @ Serial 730  
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Author (up) Facio, J.I.; Betancourth, D.; Pedrazzini, P.; Correa, V. F; Vildosola, V.; García, D. J.; Cornaglia, P.S. url  doi
openurl 
  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) Vildosola, V.; Llois, A.M.; Sereni, J.G. doi  openurl
  Title Influence of 4f hybridization on the structural and electronic properties of CeM2Si2 (M=Ru, Rh, and Pd) Type Journal Article
  Year 2004 Publication Physcal Review B Abbreviated Journal Phys. Rev. B  
  Volume 69 Issue 12 Pages 125116  
  Keywords  
  Abstract We present full potential ab initio calculations to study structural and electronic properties of CeM2Si2 with M=Ru, Rh, and Pd. Two kind of calculations are performed: one considering the 4f states as hybridized ones and another simulating Cc systems with nonhybridized 4f states. We calculate the hybridization function and analyze the influence of the 4f states on structural properties such as equilibrium volume, c/a ratio, and bulk modulus and study their evolution together with that of the spin magnetic moment under applied hydrostatic pressure. The results are compared with experimental data.  
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  Series Volume Series Issue Edition  
  ISSN 1098-0121 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000221259000042 Approved no  
  Call Number BT @ hernan @ Serial 65  
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Author (up) Vildosola, V.L.; Llois, A.M.; Weissmann, M.; Sereni, J.G. doi  openurl
  Title Magnetic behaviour of Ce(Pd1-xMx) compounds (M = Rh, Ni and Ag) within the LDA approximation Type Journal Article
  Year 2001 Publication Journal of Magnetism and Magnetic Materials Abbreviated Journal J. Magn. Magn. Mater.  
  Volume 236 Issue 1-2 Pages 6-8  
  Keywords  
  Abstract Ce intermetallic compounds have been intensively studied in the last few decades due to the large variety of behaviours they exhibit. In particular, two ways of demagnetizing Ce have been experimentally tried within the ferromagnetic systems Ce(Pd1-xMx), namely through electronic concentration variations (M=Rh) and volume reductions (M=Ni). On the other hand, when Pd is substituted by Ag, a transformation from a ferromagnetic to an antiferromagnetic ground state has been observed. In this work, we analyse the evolution of the magnetism of Ce in the above-mentioned family of compounds by calculating the spin contribution to magnetism that results from spin polarised LDA calculations. (C) 2001 Elsevier Science B.V. All rights reserved.  
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  Series Volume Series Issue Edition  
  ISSN 0304-8853 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000171670100004 Approved no  
  Call Number BT @ hernan @ Serial 75  
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