Ti-doping effects on magnetic properties of dense MgB2 bulk superconductors
Ti-doping effects on magnetic properties of dense MgB2 bulk superconductors
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DOI：
10.1088/0953-2048/28/9/095009
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发表时间：
2015-07
影响因子：
3.6
通讯作者：
T. Naito;Takafumi Yoshida;H. Fujishiro
中科院分区：
文献类型：
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作者：
T. Naito;Takafumi Yoshida;H. Fujishiro
研究了Ti掺杂对MgB_2超导块材磁性能的影响。捕获场，这是由场冷磁化，B T FC？>在13 K时，在单个Ti 5 -20%掺杂的MgB 2块体的表面处，约为3.6 T，这是未掺杂的块体的约1.3倍。B T FC？>在14.1 K时，在双堆叠的Ti掺杂的MgB 2块体的中心实现了4.6 T的温度。零场冷却磁化所产生的俘获磁场对应的剩余磁通密度B T ZFC？>在40小时内，具有约2%的非常小的涡旋蠕变速率的矫顽力的绝对值相当。这些结果表明，MgB 2块体是一个优秀的“准永磁”磁铁。临界电流密度Jc？>在磁场下，Ti掺杂也提高了Jc？> 4.0 × 10 3？原始样品的cm-2提高到1.6-1.8 × 104？对于Ti掺杂样品，为cm-2。在20 K时，Ti掺杂样品的不可逆场超过5 T。显微观察表明，在Ti掺杂块体中存在纳米级未反应的B和严重缺Mg的Mg-B颗粒以及Ti沉淀周围的TiB 2层。掺Ti的MgB 2的涡旋钉扎性能的改善源于纳米非超导粒子和TiB 2层作为强涡旋钉扎中心的产生。
We have studied the effects of Ti doping on the magnetic properties of MgB2 superconducting bulks. The trapped field, which was obtained by field-cooled magnetization, B T FC ?> , was about 3.6 T at 13 K at the surface of the single Ti5–20% doped MgB2 bulks, which was about 1.3 times larger than that of the non-doped bulk. The B T FC ?> of 4.6 T was achieved at 14.1 K in the centre of the doubly stacked Ti-doped MgB2 bulks. The remanent magnetic flux density, which corresponds to the trapped field by zero-field cooled magnetization, B T ZFC ?> , was comparable with the absolute value of coercive force with a very small vortex creep rate of about 2% over 40 h. These results suggested that the MgB2 bulk was an excellent ‘quasi-permanent’ magnet. The critical current density, J c ?> , under magnetic field was also enhanced by Ti doping; under 3 T at 20 K, the J c ?> of 4.0 × 10 3 ?> A cm−2 for the pristine sample was enhanced to that of 1.6–1.8 × 10 4 ?> A cm−2 for the Ti-doped samples. The irreversibility field exceeded 5 T at 20 K for the Ti-doped samples. The existence of nanometric unreacted B and strongly Mg-deficient Mg-B particles and TiB2 layers at the periphery of Ti precipitates was suggested in the Ti-doped bulks by microscopic observation. The improvement of the vortex pinning properties in Ti-doped MgB2 originated from the creation of the nanometric nonsuperconducting particles and TiB2 layers acting as strong vortex pinning centres.