Magnetic-Flux Trapping and Related Phenomena in Sn-Pb Solders

Superconductors have the properties of zero electrical resistance and exclusion of magnetic fields below superconducting transition temperature(<i>T</i>_c). In addition, the suppression of thermal conductivity (k)is seen below <i>T</i>_c, which is cause by the fact that the Cooper pairs do not transport heat, and the electrons conduct heat in the normal-conducting state. Recently, our group reported that a Sn45-Pb55 solder, a phase-separated superconducting composite composed of Sn and Pb, exhibits nonvolatile magneto-thermal switching. This is caused by the nonvolatility of magnetic flux trapping induced by the experience of magnetic field greater than critical field (<i>H</i>_c) of the solder[1]. Furthermore, the magneto-thermal switching properties strongly depend on the Sn/Pb concentration. Therefore, this study aims to elucidate the Sn-amount dependence of flux trapping states, magneto-thermal switching properties, and related physical properties.<br/>We measured the magnetization of SnxPb100-x solders with various Sn ratios (x = 10-90). We investigated the dependence of the flux trapping on x. In Sn10-Pb90, we found that the magnetic flux trapping is 600 G, when measured at zero field after experiencing <i>H</i> = 1500 Oe at 1.8 K. Furthermore, the magnetization decreases when a positive field is applied after experiencing <i>H</i> = 1500 Oe. For negative-field data, data measured under opposite fields against the initial <i>H</i> = 1500 Oe, we observed flux jumps[2]. With increasing x, the amount of trapped magnetic flux is reduced, which means that the concentration and the size of Sn regions are correlating with trapped field. In the presentation ,we will show the correlation between x, trapped field, and magneto-thermal switching properties for various x.<br/>[1] H. Arima et al., Commun. Mater. 5, 34 (2024).<br/>[2] Y. Mizuguchi et al., arXiv:2405.01850