Investigation the positive moments on the M-T curve of YBCO films measured by using zero-field cooling

• 来源期刊: 中国物理（英文版）
• 学科: 物理学
• 关键词: SQUID magnetometer remnant field superconducting M-T curve flux pinning positive moment superconducting paramagnetic Meissner effect
• 年，卷（期）: 2002,（4）
• 页码范围: 379-382
• 页数: 4页
• 分类号: O4
• 语种: 英文

摘要

The superconducting transition of a YBCO film was measured by a MPMS-5 superconducting quantum interference device magnetometer, using a zero-field cooling process. The experimental results have shown that there are positive magnetic moment and positive peak on the M-T curve. We have proven that these anomalous behaviours are due to measurement error, but not phase transition. We have proposed a simple formula to explain and to calculate quantitatively these anomalous behaviours. It was found that, provided dH ＞ 0.59Hp (dH is the inhomogeneous field of the remnant field, Hp is the fully penetrated field of the measured sample), the experimental results will be positive,not negative.If dH ≥ 2Hp, the experimental results will be symmetrical to their real negative values. From the M-T curve, which h as positive moment and positive peak below Tc (superconducting transition temperature), we found a new possible method to obtain Hp of the measured sample.