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Enhanced pinning in high-temperature superconducting cuprate single crystals at low DC magnetic field

Low density flux dynamics in Nd based cuprate (NdBa2Cu3O7-x) HTSC single crystals trapped in 1 Oe range DC magnetic fields were investigated for the first time. Complex measurements of time, temperature and field dependence of magnetization were performed. Using the results obtained and the Anderson-Kim model the normalized magnetization relaxation rate S and the averaged effective pinning potential U were calculated. We show a significant (one or even two orders) increase in the effective pinning potential in these samples in comparison with measurements performed in high magnetic fields for similar cuprate single crystals formerly. In a wide enough range of temperatures close to Tc (0.72 < T/Tc < 0.93) it has been shown that the doping of NdBa2Cu3O7-x single crystals with calcium atoms leads to the increase of the averaged effective pinning potential with an insignificant decreasing of the critical temperature.