Paramagnetic Meissner effect at high fields in YCaBaCuO single crystal and melt-textured YBaCuO

Abstract

a b s t r a c tWe report on systematic field-cooled magnetization experiments in an Y 0.98 Ca 0.02 Ba 2 Cu 3 O 7Àd single crystal and melt-textured YBa 2 Cu 3 O 7Àd samples. Magnetic fields up to 50 kOe were applied and a paramagnetic response related to the superconducting state was observed. We discuss our results in terms of the flux compression scenario into the sample.Ó 2010 Elsevier B.V. All rights reserved.The paramagnetic Meissner effect (PME) was first observed in polycrystalline samples of the high-T C superconductors (HTSC) [1]. The effect is attributed to the occurrence of a net paramagnetic moment when the materials are cooled through T C in the presence of low and high magnetic fields. This unusual effect seems to be superimposed to the conventional diamagnetism. Several models and explanations have been proposed. The PME has been attributed to spontaneous orbital currents which should occur in granular networks, where p junctions are randomly distributed [2], sample geometry and surface [3], nonequilibrium compressed flux states stabilized by inhomogeneous cooling [4], the formation of a giant vortex on the sample surface [5], etc. Recently, the PME has been observed in YBaCuO/LaCaMnO superlattices [6].In this paper, we report on field-cooled-cooling (FCC) magnetization measurements as functions of the temperature in an Y 0.98 Ca 0.02 Ba 2 Cu 3 O 7Àd single crystal (YCaBaCuO) and melt-textured YBa 2 Cu 3 O 7Àd (YBaCuO) samples. Magnetic fields up to H = 50 kOe were applied parallel and perpendicular to the c-axis. The melttextured YBaCuO sample was prepared by top-seeding technique [7], with 25 wt.% of Y 2 BaCuO 5 (Y211), and the single crystalline YCaBaCuO sample was grown by the self-flux method [8]. The magnetization measurements were done with a Quantum Design SQUID magnetometer. The SQUID signal and the sample centering were monitored during the experimental runs. Magnetic fields up to 50 kOe were applied either parallel or perpendicular to the ab plane in both samples. The results were corrected for the demagnetizing factor and the spin contribution from the Y211 particles was subtracted from the raw data in melt-textured sample. Fig. 1 shows the FCC magnetization measurements for the YCaBaCuO single crystalline sample in fields between 0.01 and 50 kOe applied parallel to the c-axis. In Fig. 1 we observe that, at the lowest applied field, the moment is diamagnetic, but the diamagnetism decreases when the field is augmented. When the field magnitude reaches about 5 kOe the magnetic moment shows a sign reversal. For higher fields, the FC magnetization becomes increasingly positive, as illustrated by results obtained at H = 50 kOe. A small diamagnetic dip always occurs nearly below T C in experiments performed in this field range. The experiments were repeated and the results were confirmed. Similar results were obtained when the magnetic field was applied parallel to the ab plane. Fig. 2 shows the FCC magnetization measurements for the melt-textured YBaCuO sample in fields between 0.05 and 50 k...

Functional behavior of the anomalous magnetic relaxation observed in melt-textured YBa2Cu3O7-δ samples showing the paramagnetic Meissner effect

“…2, are a clear evidence of relaxation processes occurring in our samples. Similar results can be found in the literature [7,13,14,17,20,24]. On the other hand, when low magnetic fields are applied, the magnetic flux compression mechanism is weaker than the conventional Meissner effect, and a diamagnetic moment can be observed, such as shown in the inset of the Fig.…”

“…According to this idea, a strong nonequilibrium compressed flux state could be originated and stabilized by an inhomogeneous cooling of the superconducting material below TC. In this scenario, that can be possible in small samples, and even in single crystals [7,13,14,17], the surface of the material could become superconducting before the bulk and the magnetic flux could be expelled outside or inside the material. As a possible consequence, if the magnetic flux is expelled inside the material it could be pushed into its interior, originating a flux compressed state, that can be stabilized by pinning centers, in our case the Y211 phase.…”

“…Originally the PME was observed in polycrystalline samples of high temperature superconductors [1,2], however, the effect has been observed in several superconducting systems and under different magnetic field ranges [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. A curious and interesting feature is the anomalous time dependence of the FC magnetic moment observed in some superconducting samples [7,13,14,19,20]. This behavior manifests itself as a strong paramagnetic relaxation, contrasting with the expected diamagnetic relaxation.…”

Magnetical Response and Mechanical Properties of High Temperature Superconductors, YBaCu3O7-X Materials

“…Recently, the high-field PME was also observed in an Y 0.98 Ca 0.02 Ba 2 Cu 3 O 7-x single crystal (Dias et al, 2010), and the results were attributed to strong flux compression state into the sample modulated by pinning. An important review of the paramagnetic Meissner effect and related dynamical phenomena was presented by M.S.…”

“…Recently, the PME has been also observed in Pb films by Brandt et al (Brandt et al, 2011). The effect can be observed in polycrystalline sintered samples (Svendlindh et al, 1989), melt-textured samples (Pureur et al, 2001), single-crystals (Kusmartsev et al, 1997;Dias et al, 2010), alloys (Schwartz et al, 2006) and thin films (Pan et al, 2006;Terentiev et al, 1999) prepared by several techniques.…”