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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 | |
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| 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 |
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 | |
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| 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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Carreras Oropesa, W.G.; Correa, V.F.; Sereni, J.G.; García, D.J.; Cornaglia, P.S. | ||||
| Title | Landau theory for magnetic and structural transitions in CeCo0.85Fe0.15Si | Type | Journal Article | ||
| Year | 2018 | Publication | Journal of Physics: Condensed Matter | Abbreviated Journal | J. Phys.: Condens. Matter |
| Volume | 30 | Issue | Pages | 295803 | |
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| Abstract | We present a phenomenological analysis of the magnetoelastic properties of CeCo0.85Fe0.15Si at temperatures close to the Néel transition temperature TN. Using a Landau functional we provide a qualitative description of the thermal expansion, magnetostriction, magnetization and specific heat data. We show that the available experimental results (Correa et al 2016 J. Phys.: Condens. Matter 28 346003) are consistent with the presence of a structural transition at Ts TN and a strong magnetoelastic coupling. The magnetoelastic coupling presents a Janus-faced effect: while the structural transition is shifted to higher temperatures as the magnetic field is increased, the resulting striction at low temperatures decreases. The strong magnetoelastic coupling and the proximity of the structural transition to the onset temperature for magnetic fluctuations, suggest that the transition could be an analogue of the tetragonal to orthorhombic observed in Fe-based pcnictides. |
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| Call Number | BT @ victor.correa @ | Serial | 796 | ||
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Carreras Oropesa, W.G.; Encina, S.; Pedrazzini, P.; Correa, V.F.; Sereni, J.G.; Vildosola, V.; García D.J.; Cornaglia, P.S. | ||||
| 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 |
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 | |
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| 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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| Notes | Approved | no | |||
| Call Number | BT @ victor.correa @ | Serial | 842 | ||
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| Author |
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. | ||||
| 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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Facio, J.I.; Abate, A.; Guimpel, J.; Cornaglia, P.S. | ||||
| Title | Vortex kinks in superconducting films with periodically modulated thickness | Type | Journal Article | ||
| Year | 2013 | Publication | Journal of Physics: Condensed Matter | Abbreviated Journal | J. Phys.: Cond. Matter |
| Volume | 25 | Issue | 24 | Pages | 245701 |
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| Abstract | We report magnetoresistance measurements in Nb films having a periodic thickness modulation. The cylinder shaped thicker regions of the sample, which form a square lattice, act as repulsive centers for the superconducting vortices. For low driving currents along one of the axes of the square lattice, the resistivity Ï increases monotonously with increasing magnetic field B and the Ï– B characteristics are approximately piecewise linear. The linear Ï versus B segments change their slope at matching fields where the number of vortices is an integer or a half integer times the number of protruding cylinders in the sample. Numerical simulations allow us to associate the different segments of linear magnetoresistance to different vortex-flow regimes, some of which are dominated by the propagation of discommensurations (kinks). | ||||
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| ISSN | 0953-8984 | ISBN | Medium | ||
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| Notes | Approved | no | |||
| Call Number | BT @ pedrazp @ | Serial | 672 | ||
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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 | |
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| 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 |
García, D.J.; Franco, D.G.; Cornaglia, P.S. | ||||
| Title | Large magnetocaloric effect in the frustrated antiferromagnet EuIr2P2 | Type | Journal Article | ||
| Year | 2023 | Publication | Journal of Magnetism and Magnetic Materials | Abbreviated Journal | J. Magn. Magn. Mater. |
| Volume | 565 | Issue | Pages | 170307 | |
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| Abstract | We present a theoretical analysis of the magnetocaloric effect in the frustrated antiferromagnet EuIrP. Monte Carlo simulations indicate a large magnetic entropy change J kg−1 K−1 at K for a moderate change in the external magnetic field Tesla. The highest value of seems to be associated with the presence of a multicritical point in the magnetic field versus temperature phase diagram (at Tesla and K) but it persists with similar large values for a broad range of temperatures . Single crystal EuIrP magnetization vs magnetic field experiments allowed us to obtain the magnetocaloric effect for K. The results are consistent with the theoretical analysis and show a large magnetocaloric effect for K. Finally, we present a phenomenological Landau functional analysis that provides a simplified description of the phase diagram and of the magnetocaloric effect. Although the magnetic frustration in this system leads to a rich phase diagram, we found no clear indication that it plays a significant role enhancing the magneticaloric effect, other than by reducing the transition temperatures and fields. | ||||
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| ISSN | 0304-8853 | ISBN | Medium | ||
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| Notes | Approved | no | |||
| Call Number | BT @ pedrazp @ | Serial | 897 | ||
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