Braun, E., A. Bürger, B. Roden, and J. G. Sereni. "Spin glass-like behaviour of the singlet ground state system: ThTb." Solid State Communications 66, no. 11 (1988): 1141–1144.
Abstract: We have studied the temperature and field dependence of the magnetic susceptibility, X, on the single-ground-state Th1?nTbn system, in the 0.2 < n < 0.6 concentration range. The characteristic maximum of a spin glass transition was found at a temperature Tg, which increases linearly with the impurity concentration. As expected, the maximum of X is reduced by the increment of the applied magnetic field. The spin glass order parameter, as well as its critical exponent were evaluated by using the Sherrington-Kirkpatrick theory.
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Durán, C., P. Esquinazi, C. Fainstein, and M. Núñez Regueiro. "Anomalies in the internal friction and sound velocity in YBa2Cu3O7-x and EuBa2Cu3O7-x superconductors." Solid State Communications 65, no. 9 (1988): 957–961.
Abstract: Internal friction Q-1 and Young Modulus sound velocity vE measurements at 1 kHz in YBa2Cu3O7?x and EuBa2Cu3O7?x polycrystalline samples reveal anomalies at the superconducting transition and at not, vert, similar37 K. The anomaly in vE at not, vert, similar90 K is accompanied by an absorption peak and is in agreement with published ultrasonic measurements, suggesting a lattice deformation at the superconducting transition.
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Civale, L., H. Pastoriza, F. de la Cruz, J. Guimpel, G. Nieva, J. M. Heintz, O. Durmeyer, and J. P. Kappler. "Meissner fraction of insulating samples of oxide superconductors." Solid State Communications 72, no. 4 (1989): 341–344.
Abstract: The tendency towards superconducting granularity with sample degradation is a common feature of oxide superconductors. We present magnetic, transport and calorimetric results in LiTi$2Ο4$ which show that the topological tendency to segregate the superconducting state into islands surrounded by thin insulating layers is related to the structure of the material rather than to a mechanism associated to high T$_C$. We emphasize that insulating samples with small Meissner fraction can have a superconducting volume fraction close to unity.
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Decca, R., E. Osquiguil, F. de la Cruz, C. D'Ovidio, M. T. Malachevski, and D. Esparza. "Non linear temperature dependence of the resistivity of LaSrCuO: Effects of Sr content." Solid State Communications 69, no. 4 (1989): 355–357.
Abstract: The linear temperature dependence of the electrical resistivity has been taken to be one of the characteristic features of the ceramic superconductors. Measurements of the electrical resistance of the LaSrCuO system in a wide temperature range show that the previous statement is only an approximation valid for some values of the Sr concentration.
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Rodriguez, E., J. Luzuriaga, M. Núñez Regueiro, and C. Fainstein. "Low temperature internal friction peak in high Tc superconductors." Solid State Communications 77, no. 10 (1991): 777–780.
Abstract: We measure the internal friction Q-1 in YBa2Cu3O7-x and Bi2Sr2CaCu2O8+x samples. At temperatures near 35 K for KHz frequencies we observe an attenuation peak. In the case of YBa2Cu3O7-x, assuming a thermally activated relaxation behaviour, we are able to show that it corresponds to the same process as other peaks observed at higher frequencies. For Bi2Sr2CaCu2O8+x this is not the case, and the origin of the peak, found in all the measured samples, remains unknown.
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Castello, D., M. Jaime, and M. Núñez Regueiro. "Thermal conductivity of high temperature superconductor TlBaCaCuO." Solid State Communications 79, no. 11 (1991): 967–970.
Abstract: We have measured the thermal conductivity of ceramic samples of TlBaCaCuO between 2 and 250 K. At high temperatures it follows a constant behaviour down to the superconducting transition temperature where a sudden increase of the thermal conductivity occurs, attributed to reduced phonon scattering by condensating electrons. At low temperatures a T2 law is observed, confirming the assumption that it is a common feature in most of the high temperature superconducting oxides. Phonon scattering against tunneling systems analogous to those found in amorphous solids can explain this behaviour.
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Trovarelli, O., P. Stickar, J. G. Sereni, G. Schmerber, and J. P. Kappler. "Coexistence of magnetic and non magnetic states in Ce14X51 (X = Au, Ag and Cu)." Solid State Communications 89, no. 5 (1994): 421–424.
Abstract: Magnetic (chi), thermal(C-p), and transport (p) measurements on Ce(l4)X(51) (X = Au, Ag and Cu) are presented. All these compounds show antiferromagnetic type order at low temperatures, with T-N = 0.9 K (Au), 1.1 K (Ag) and 3.2 K (Cu). Within the Gd14Ag51-type structure the Ce atoms sit in different sublattices denoted by I (2 atoms), II (6 atoms) and III (6 atoms), therefore the results can be interpreted in terms of three different behaviors of Ce depending on its local environment. From the entropy involved in the magnetically ordered (MO) phase it can be established that the Ce-II and Ce-III atoms order in Cel4Au51 and Ce14Ag51, while the Ce-I order in Cel4Cu51. There is a large linear contribution to Cp at T > T-N,T-gamma HT = 0.81 (Au), 1.24 (Ag) and 3.1 (Cu) J/mol K-2, which indicates the coexistence of MO and heavy fermions. In the case of Cel4Cu51, the magnetic contribution to Cp from sublattice Ce-I around T-N,T- resembles that of a modulated system and the characteristic temperatures for Ce-II and Ce-III atoms are estimated from p(T) as:T-K=16 K and >120 K respectively.
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Grigera, S. A., E. Morré, E. Osquiguil, G. Nieva, and F. De la Cruz. "Nonlocal transport properties and size effects in heavily twinned YBa2Cu3O7-delta single crystals." Solid State Communications 107, no. 7 (1998): 335–339.
Abstract: We demonstrate experimentally that when the vortex correlation length in the liquid state becomes of the order of the sample thickness, size effects dominate the transport properties of the macroscopic vortex structures, implying a nonlocal response in the transformer experiments.
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Herbsommer, J. A., V. F. Correa, G. Nieva, H. Pastoriza, and J. Luzuriaga. "Vortex dynamics in Bi2Sr2CaCu2O8+δ single crystals with planar defects." Solid State Communications 120, no. 2-3 (2001): 59–63.
Abstract: We have studied the effects of c-axis correlated planar defects on the vortex lattice of Bi$2$Sr$2$CaCu$2Ο8$ single crystals using Bitter decoration, transverse ac permeability and X-ray measurements. Our results show that the low field low temperature phase coherent vortex lattice exhibits anisotropic pinning in the presence of these planar defects. Frequency dependent ac permeability measurements show that the ordered solid-liquid transition is first order as in samples free of correlated defects. However, the melting point is detected only when the excitation field is along the defects.
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Fasano, Y., M. de Seta, M. Menghini, H. Pastoriza, and F. de la Cruz. "Imaging the structure of the interface between symmetries interconnected by a discontinuous transition." Solid State Communications 128, no. 3-4 (2003): 51–55.
Abstract: We have been able to observe with single particle resolution the interface between two structural symmetries that cannot be interconnected by a continuous transition. By means of an engineered 2D potential that pins the extremity of vortex strings a square symmetry was imposed at the surface of a 3D vortex solid. Using the Bitter decoration technique and on account of the continuous vortex symmetry, we visualize how the induced structure transforms along the vortex direction before changing into the expected hexagonal structure at a finite distance from the surface.
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