Temperature dependence of the minimum in AC power losses of (Nb0.99Zr0.01)3Sn in parallel AC and DC magnetic fields

ac losses PL of bronze-processed (Nb0.99Zr0.01)3Sn strips have been measured between 4.2 and 16.5 K in the presence of a dc magnetic field H0. The measurements were performed using an electronic wattmeter with both ac and dc fields parallel to the long flat surfaces of the sample. A minimum in the function PL(H0) was observed for fixed ac amplitudes h0. This minimum was found to occur in the entire temperature range between 4.2 and 16.5 K. A similar minimum was recently reported in Nb3Ge [Thompson et al., J. Appl. Phys. 50, 3514 (1979)] at 4.2 K. The position of the minimum is explained here by the same physical model as in Thompson et al. [J. Appl. Phys. 50, 3514 (1979)]; and Clem (ibid. 3518), but extending the model to include the temperature dependence of the entry surface shielding fields ΔHen(B,T) for flux density in the sample B=0. It is also shown here that loss minimum measurements can be used for the determination of ΔHen(0,T) in the temperature range 4.2–16.5 K.