GERENCIA DE ÁREA INVESTIGACIÓN, DESARROLLO E INNOVACIÓN (GAIDI)

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Examinando GERENCIA DE ÁREA INVESTIGACIÓN, DESARROLLO E INNOVACIÓN (GAIDI) por Materia "ALEACIONES"

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    ÍtemAcceso Abierto
    Bulk-like behavior in the temperature driven martensitic transformation of Cu-Zn-Al thin films with 2H structure
    (Elsevier, 2014-04-05) Haberkorn, N.; Condó, A.M.; Espinoza, C.; Jaureguizahar, S.; Guimpel, J.; Lovey, F.C.; Gerencia Física. Departamento Materia Condensada. División Bajas Temperaturas
    This paper reports on the possibility to obtain Cu–Zn–Al films with 2H martensitic structure by fixing the valence electron concentration per atom (e/a) ≈1.53. Films with thickness of ≈5 μm with micrometric grains show martensitic transformation temperature and hysteresis values close to the ones found in bulk samples. This result is different to the one found in Cu–Zn–Al thin films with 18R martensitic structure and similar microstructure, in which the hysteresis presents an increment (≈10 times) compared to bulk samples. This difference can be associated to the intrinsic nature of the 2H transformation which requires more undercooling to produce the nucleation of the martensitic phase. The driving force for the burst-type martensitic transformation decreases the influence of the microstructure in the transformation.
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    ÍtemAcceso Abierto
    Ferromagnetic quantum criticality in the alloy CePd1-xRhx
    (American Physical Society, 2007-01-31) Sereni, J.G.; Westerkamp, T.; Kuchler, R.; Caroca-Canales, N.; Gegenwart, P.; Geibel, C.; Gerencia Física. Departamento Materia Condensada. División Bajas Temperaturas
    The CePd1−xRhx alloy exhibits a continuous evolution from ferromagnetism (TC=6.5K) at x=0 to a mixed-valence (MV) state at x=1. We have performed a detailed investigation on the suppression of the ferromagnetic (F) phase in this alloy using dc (χdc) and ac (χac) susceptibility, specific heat (Cm), resistivity (ρ), and thermal expansion (β) techniques. Our results show a continuous decrease of TC(x) with negative curvature down to TC=3K at x∗=0.65, where a positive curvature takes over. Beyond x∗, a cusp in χac is traced down to T∗C=25mK at x=0.87, locating the critical concentration between x=0.87 and 0.90. The quantum criticality of this region is recognized by the −log(T∕T0) dependence of Cm∕T, which transforms into a T−q (q≈0.5) one at x=0.87. At high temperature, this system shows the onset of valence instability revealed by a deviation from Vegard’s law (at xV≈0.75) and increasing hybridization effects on high-temperature χdc and ρ(T). Coincidentally, a Fermi liquid contribution to the specific heat (γ) arises from the MV component, which becomes dominant at the CeRh limit. In contrast to antiferromagnetic systems, no Cm∕T flattening is observed for x>xcr but, rather, the mentioned power-law divergence, which coincides with a change of sign of β(T). The coexistence of F and MV components and the sudden changes in the T dependencies are discussed in the context of randomly distributed magnetic and Kondo couplings.
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    ÍtemAcceso Abierto
    Searching for a Quantum Critical Point in Rh doped ferromagnetic Ce2. 15Pd1. 95In0.9
    (IOP Publishing, 2012-00-00) Sereni, J.G.; Giovannini, M.; Gómez Berisso, M.; Saccone, A.; Gerencia Física. Departamento Materia Condensada. División Bajas Temperaturas
    Low temperature magnetic and thermal (Cm) properties of the ferromagnetic (FM) alloys Ce2.15(Pd1−xRhx)1.95In0.9 were investigated in order to explore the possibility for tuning towards a quantum critical point (QCP) by doping Pd with Rh. As expected, the magnetic transition decreases from T = 4.1K at x = 0 with increasing Rh concentration. However, the phase boundary splits into two transitions, the upper being antiferromagnetic (AF) whereas the lower FM. The AF phase boundary extrapolates to TN= 0 for xcr ≈ 0.65 whereas the first order FM transition vanishes at x ≈ 0.3. The quantum critical character of the TN → 0 point is inferred from the divergent T dependence of the tail of Cm/T observed in the x = 0.5 and 0.55 alloys, and the tendency to saturation of the maximum of Cm (TN)/T currently observed in exemplary Ce compounds when TN → 0. Beyond the critical concentration the unit cell volume deviates from the Vegard's law in coincidence with a strong increase of the Kondo temperature.
  • Miniatura
    ÍtemAcceso Abierto
    Suppression of the Shastry-Sutherland phase driven by electronic concentration reduction in magnetically frustrated Ce2.15Pd1.95(Sn1-yIny)0.9 alloys
    (American Physical Society, 2019-08-14) Sereni, J.G.; Roberts, J.; Gastaldo, F.; Giovannini, M.; Gerencia Física. Departamento Materia Condensada. División Bajas Temperaturas
    Exploiting the possibility to switch from antiferromagnetic (AFM) and ferromagnetic (FM) ground states (GSs) in out-stoichiometric branches of Ce2Pd2In alloys, the stability of Shastry-Sutherland (ShSu) phase of Ce2Pd2Sn as a function of Sn/In electron doping was studied. Magnetic and specific-heat measurements show that the Ce-rich compositions stabilize the FM-GS throughout the Sn/In-FM substitution, allowing to extend the formation of the ShSu phase up to its collapse in a tricritical point around ycr=0.5. On the other hand, this behavior is quite different from that reported in a recent investigation on the AFM branch where atomic disorder at intermediate Sn/In-AFM concentrations inhibits the formation of the ShSu phase.