A magnetic field relaxation at the center of a pulse-magnetized single-domain Y-Ba-Cu-O superconductor at 78K has been studied. In case of a weak magnetization, the magnetic flux density increases logarithmically and normalized relaxation rate defined as S=-d(lnB)/d(lnt) is negative (S=-0.037). When an external magnetic field magnitude increases, the relaxation rate first decreases in absolute value, then changes sign (becomes positive, S>0) and after reaching some maximum finally reduces to a very small value. Non-monotonous dependence of S vs Ha is explained by a non-homogeneous local temperature distribution during a pulse magnetization.
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