Magnetic properties of ? ceramics

Magnetic properties of a series of Mg-doped 0953-2048/11/8/008/img10 granular samples were studied by means of vibrating-sample and SQUID magnetometry. The equilibrium moment 0953-2048/11/8/008/img11 measured after the sample demagnetization gave evidence that the surface barrier effects can be neglected up to 60 K. Slope of the high-field 0953-2048/11/8/008/img12 dependence was used for determination of the temperature dependence of the penetration depth 0953-2048/11/8/008/img13 and its extrapolation to T = 0, 0953-2048/11/8/008/img14. The latter quantity was found to be significantly affected by the expression used for the data fit. The irreversible moment 0953-2048/11/8/008/img15 deduced from the magnetic hysteresis loops showed a pronounced fishtail effect. In the temperature range 50-60 K, the 0953-2048/11/8/008/img16 curve was found to scale in a similar manner as in (RE)-123 single crystals. The conventional relaxation rate dramatically changes at the fields around the remanent state. The field range of this anomaly coincides with the central peak width, and we attribute this effect to redistribution of the magnetic flux in the sample. A simple non-monotonic dependence was observed of the fishtail maximum position on the nominal Mg content. A similar but mirror dependence was found of 0953-2048/11/8/008/img17.