Modification of Critical Current Density Anisotropy in High-<i>T</i>_c Superconductors by Using Heavy-Ion Irradiations

• Main Author: Tetsuro Sueyoshi
• Format: Article
• Language: English
• Published: MDPI AG 2021-05-01
• Series: Quantum Beam Science
• Subjects: high-<i>T</i>_c superconductors; critical current density; flux pinning; heavy-ion irradiation; columnar defects; anisotropy
• Online Access: https://www.mdpi.com/2412-382X/5/2/16

The critical current density <i>J</i>_c, which is a maximum value of zero-resistivity current density, is required to exhibit not only larger value but also lower anisotropy in a magnetic field <i>B</i> for applications of high-<i>T</i>_c superconductors. Heavy-ion irradiation introduces nanometer-scale irradiation tracks, i.e., columnar defects (CDs) into high-<i>T</i>_c superconducting materials, which can modify both the absolute value and the anisotropy of <i>J</i>_c in a controlled manner: the unique structures of CDs, which significantly affect the <i>J</i>_c properties, are engineered by adjusting the irradiation conditions such as the irradiation energy and the incident direction. This paper reviews the modifications of the <i>J</i>_c anisotropy in high-<i>T</i>_c superconductors using CDs installed by heavy-ion irradiations. The direction-dispersion of CDs, which is tuned by the combination of the plural irradiation directions, can provide a variety of the magnetic field angular variations of <i>J</i>_c in high-<i>T</i>_c superconductors: CDs crossing at ±<i>θ</i>_i relative to the <i>c</i>-axis of YBa₂Cu₃O_y films induce a broad peak of <i>J</i>_c centered at <i>B</i> || <i>c</i> for <i>θ</i>_i < ±45°, whereas the crossing angle of <i>θ</i>_i ≥ ±45° cause not a <i>J</i>_c peak centered at <i>B</i> || <i>c</i> but two peaks of <i>J</i>_c at the irradiation angles. The anisotropy of <i>J</i>_c can also modified by tuning the continuity of CDs: short segmented CDs formed by heavy-ion irradiation with relatively low energy are more effective to improve <i>J</i>_c in a wide magnetic field angular region. The modifications of the <i>J</i>_c anisotropy are discussed on the basis of both structures of CDs and flux line structures depending on the magnetic field directions.