Abstract
The amplitude-dependent internal friction of diamagnetic copper and lead polycrystals 99.9% pure has been studied experimentally in dc magnetic fields with an induction 0 ≤ B ≤ 0.75 T. In a dc magnetic field B = 0.1 T at room temperature, the sign inversion (from plus to minus) of internal-friction increments ΔQ−1(B) = Q−1(B) − Q−1(0) is revealed for two copper samples. The copper contained impurity-pinned dislocations at ΔQ−1(B) > 0 and impurity-free dislocations at ΔQ−1(B) < 0. The positive sign of ΔQ−1(B) for the internal friction in copper is due to a decrease in the potential-barrier height Ub for dislocation motion in impurity-containing metals. The negative sign of ΔQ−1(B) for the internal friction in copper is due to a simultaneous decrease in the barrier height Ub and width (activation volume Θ) during dislocation motion in impurity-containing metals. For a magnetic field B = 0.1 T, the sign of ΔQ−1(B) in lead is positive at temperatures below 70°C and the sign of ΔQ−1(B) is negative at temperatures above 70°C. For lead, the sign inversion of ΔQ−1(B) is explained by the dissolution of dislocation impurity atmospheres at temperatures higher than 70°C.
Published Version
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