Abstract
We have measured magnetic relaxation M versus time in a twin-free single crystal of for magnetic fields applied parallel to a - b planes. Magnetic relaxation is studied as a function of temperature (T) for a fixed field (H) and at a fixed T as a function of H. Long-time M versus t curves were mainly obtained for the partial field penetrating regime. All log M versus log t curves obtained in the partial-field regime present a kink at time separating two distinct regions. The kink gradually disappears as the applied field fully penetrates the sample. The value of is constant for all field values. Similar but more accentuated differences are observed when the effective activation energy U extracted from the data is plotted against M(t). A linear behaviour of U with M is observed in the full field penetrated regime. We estimate that the Bean penetration depth increases exponentially with H in the partial-field regime. We also determined the range of temperatures for which surface barriers are important at the initial stage of relaxation.
Published Version
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