Effect of the hot pressing on the magnetic-field and temperature dependences of flux pinning for SiC-doped MgB₂ tape

To understand the effects of the hot pressing on the pinning behavior for the SiC doped MgB₂ tape wire, magnetic field and temperature dependences on a critical current density J_c and the pinning force have been studied. The MgB₂ tapes were fabricated using an in situ powder-in-tube (PIT) method, the hot pressing process with nano-SiC powders and the carbon steel sheath. J_c of the hot pressing processed wire is enhanced especially at low field compared with that of the no hot-pressed wire. It is suggested that the enhancement of J_c is caused by the improvement of the MgB₂ grain connectivity came from the hot pressing. The pinning analysis using the pinning models of a surface pinning and a normal point pinning lead to that the scaled curve of the pinning force for the SiC-doped MgB₂ tape with the hot pressing process showed anisotropy in a lower field. This result suggests that the pinning center of the hot pressing processed MgB₂ wire forms into inequi-axial shape, which is different from that in the tape without the hot pressing having the equi-axial pinning center in our previous report. It was also found that the scaled pinning force of the SiC-doped MgB₂ tape with the hot pressing is larger than the surface pinning model in a higher field. This suggests that the pinning force was enhanced by the hot pressing in a higher field.