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Sereni, J. G., G. Schmerber, M. G. Berisso, B. Chevalier, and J. P. Kappler. "Tricritical point and suppression of the Shastry-Sutherland phase in Ce2(Pd1−xNix)2Sn." Physical Review B – Condensed Matter and Materials Physics 85, no. 13 (2012): 134404.
Abstract: Structural, magnetization, and heat capacity measurements were performed on Ce2(Pd1−xNix)2Sn compounds covering the full range of the Mo2FeB2 structure stability (0⩽x⩽0.25). In this system, the two transitions observed in Ce2Pd2Sn (antiferromagnetic TN=4.8 K and ferromagnetic TC=2.1 K) converge into a tricritical point at Tcr≈3.4 K for xcr≈0.3, where the intermediate antiferromagnetic (AF) phase is suppressed. The decrease of the TN(x) phase boundary is due to an incipient Kondo screening of the Ce-4f moments. This effect and the increase of local atomic disorder affect the formation of Ce-magnetic dimers on which the Shastry-Sutherland lattice (SSL) builds up. On the contrary, the TC(x) transition to the ferromagnetic ground state increases as a consequence of the weakening of the intermediate phase. Applied magnetic fields also suppress the AF-SSL phase as it was already observed in the stoichiometric compound.
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Sereni, J. G., M. Gómez Berisso, G. Schmerber, and J. P. Kappler. "Suppression of the Shastry-Sutherland phase in Ce2 Pd 2 Sn at a field-induced critical point." Physical Review B – Condensed Matter and Materials Physics 81, no. 18 (2010): 184429.
Abstract: The magnetic phase diagram of Ce2 Pd2 Sn is investigated through the field dependence of thermal, transport, and magnetic properties at low temperature. The upper transition, TM =4.8 K is slightly affected by magnetic field up to B=1 T whereas the lower one T C (B) rapidly increases from 2.1 K joining TM in a critical point at Tcr = (4.1±0.2) K for Bcr = (0.11±0.01) T. At that point, the intermediate phase, previously described as an unstable Shastry-Sutherland lattice, is suppressed. A detailed analysis around the critical point reveals a structure in the maximum of the ∂ M/∂ B (B) derivative, which may be related to a step in magnetization predicted by theory for the mentioned lattice. © 2010 The American Physical Society.
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Sereni, J. G., M. Gomez Berisso, A. Braghta, G. Schmerber, and J. P. Kappler. "Unstable Shastry-Sutherland phase in Ce2Pd2Sn." Physical Review B – Condensed Matter and Materials Physics 80, no. 2 (2008): 022428.
Abstract: Thermal (CP) , magnetic ( M and χac ), and transport (Ï) 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 Ï(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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R. Nath, Y. Furukawa, F. Borsa, E. E. Kaul, M. Baenitz, C. Geibel y D. C. Johnston. "Single crystal 31P NMR studies of the frustrated square lattice compound Pb2VO(PO4)2." Physical Review B – Condensed Matter and Materials Physics 80 (2009): 214430.
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R. Nath, A. A. Tsirlin, E. E. Kaul, M. Baentiz, N. Buettgen, H. Rosner y C. Geibel. "Strong frustration due to competing ferro- and antiferromagnetic interactions: magnetic properties of M(VO)2(PO4)2 (M = Ca and Sr)." Physical Review B – Condensed Matter and Materials Physics 78 (2008): 024418.
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Lee, S. - C., M. Sullivan, G. R. Ruchti, S. M. Anlage, B. S. Palmer, B. Maiorov, and E. Osquiguil. "Doping-dependent nonlinear Meissner effect and spontaneous currents in high-Tc superconductors." Physical Review B – Condensed Matter and Materials Physics 71, no. 1 (2005).
Abstract: We measure the local harmonic generation from superconducting thin films at microwave frequencies to investigate the intrinsic nonlinear Meissner effect near Tc in the zero magnetic field. Both second and third harmonic generation are measured to identify time-reversal symmetry breaking (TRSB) and time-reversal symmetric (TRS) nonlinearities. We perform a systematic doping-dependent study of the nonlinear response and find that the TRS characteristic nonlinearity current density scale follows the doping dependence of the depairing critical current density. We also extract a spontaneous TRSB characteristic current density scale that onsets at Tc, grows with decreasing temperature, and systematically decreases in magnitude (at fixed T/TC) with underdoping. The origin of this current scale could be Josephson circulating currents or the spontaneous magnetization associated with a TRSB order parameter.
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Valenzuela, S. O., B. Maiorov, E. Osquiguil, and V. Bekeris. "Elastic-to-plastic crossover below the peak effect in the vortex solid of YBa2Cu3O7 single crystals." Physical Review B – Condensed Matter and Materials Physics 65, no. 6 (2002): 605041–605044.
Abstract: We report on transport and ac susceptibility studies below the peak effect in twinned YBa2Cu3O7 single crystals. We find that disorder generated at the peak effect can be partially inhibited by forcing vortices to move with an ac driving current. The vortex system can be additionally ordered below a well-defined temperature where elastic interactions between vortices overcome pinning-generated stress and a plastic-to-elastic crossover seems to occur. The combined effect of these two processes results in vortex structures with different mobilities that give place to history effects.
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Maiorov, B., and E. Osquiguil. "Vortex solid state in YBa2Cu3O7-? twinned crystals." Physical Review B – Condensed Matter and Materials Physics 64, no. 5 (2001): 0525111–0525114.
Abstract: We report on the scaling of transport properties around the vortex melting in YBa2Cu3O7-? oriented-twin single crystals in applied magnetic fields between 1 T and 18 T. We find that for the whole measured field range the linear resistivity scales as ?(t,?)?tsyF
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Maiorov, B., G. Nieva, and E. Osquiguil. "First-order phase transition of the vortex lattice in twinned YBa2Cu3O7 single crystals in tilted magnetic fields." Physical Review B – Condensed Matter and Materials Physics 61, no. 18 (2000): 12427–12432.
Abstract: We present an exhaustive analysis of transport measurements performed in twinned YBa2Cu3O7 single crystals which establishes that the vortex solid-liquid transition is first order when the magnetic field H is applied at an angle ? away from the direction of the twin planes. We show that the resistive transitions are hysteretic and the V-I curves are nonlinear, displaying a characteristic S shape at the melting line Hm(T), which scales as ?(?)Hm(T,?), where ?(?) is the anisotropy factor. These features are gradually lost when the critical point H*(?) is approached. Above H*(?) the V-I characteristics show a linear response in the experimentally accessible V-I window, and the transition becomes reversible. Finally we show that the first-order phase transition takes place between a highly correlated vortex liquid in the field direction and a solid state of unknown symmetry. As a consequence, our data support the scenario for a vortex-line melting in twinned YBa2Cu3O7 crystals in contrast to a vortex sublimation as recently suggested for untwinned La2-xSrxCuO4, YBa2Cu3O7 and Bi2Sr2CaCu2O8 [T. Sasagawa et al., Phys. Rev. Lett. 80, 4297 (1998)].
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Fainstein, A., B. Maiorov, J. Guimpel, G. Nieva, and E. Osquiguil. "Annealing disorder and photoinduced order of oxygen chains in detwinned YBa2Cu3O6.65 single crystals probed by Raman scattering." Physical Review B – Condensed Matter and Materials Physics 61, no. 6 (2000): 4298–4304.
Abstract: Raman scattering in detwinned YBa2Cu3O6.65 single crystals is studied as a function of photoexcitation and annealing. Copper-oxygen chain-related forbidden Raman bands that are known to strongly bleach with illumination at low temperatures, increase their intensity with chain fragmentation induced by annealing at high temperature. This contrasting behavior proves the conjunction of short Cu-O fragments into longer chains on photoexcitation. We interpret the Raman modes as due to vibrations at the end of CuO chain fragments and Cu-O-Cu monomers, and use their evolution with illumination and annealing as anisotropic sensitive markers of oxygen reordering processes. The identification of the “forbidden” Raman bands is discussed in the context of our results and recent literature in the subject. We also present absorption measurements performed on GdBa2Cu3Ox thin films with varying oxygen content. These experiments show that the 2.2-eV absorption and the chain-related Raman peaks have different dependencies with oxygen content and illumination, ruling out an explanation that suggests that the Raman intensity reduction of these modes is due to a photobleaching of intermediate defect states. These results highlight the potentialities of Raman scattering for oxygen dynamics studies and demonstrate the presence of photoinduced oxygen ordering in these high-Tc superconductor compounds.
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