Giant Magneto Impedance Effect of Co-Based Metallic Fiber Under Bias Magnetic Field

The giant magneto impedance, GMI, effect of Co-based metallic fibers prepared by melt-extracted technology is investigated under different bias direct electrical current Ib. The GMI curves have single peaks which are symmetric about zero field at and below 1MHz. However, the bimodal GMI curves which have asymmetric peaks are observed when Ib is over 2mA at 0.1MHz. And asymmetric GMI, AGMI, effect is also appeared at 1MHz when Ib just is 1mA and the field sensitivity of GMI effect is increased 5.6 times. The GMI effect and magnetization process is affected by the bias magnetic field profoundly induced by Ib, which is correlated with the outer shell domain structures with circumferentially magnetization easy axis existed in the outer shell of Co-rich magnetic wires with low and negative magnetostriction. Below 1 MHz, only if the bias current is over 1.5mA which induces a magnetic circumferential magnetic field is above the coercivity of 14.4A/m, the circumferential magnetization and GMI effect can experience the bias magnetic field effect. Above 1MHz, the skin effect gets stronger and significantly decreases the total participants of circular magnetization process in the fibers and consequently, the circular outer shell magnetization process gets much sensitive to circular bias magnetic field. AGMI effect with high field sensitivity is realized due to the bias current.

本文研究了熔融萃取工艺制备的钴基金属纤维在不同偏置直流电流Ib作用下的巨磁阻抗（Giant Magneto Impedance, GMI）效应。在1MHz及更低频率下，GMI曲线呈现单峰形态，且关于零磁场对称。然而，在0.1MHz频率下当Ib超过2mA时，可观测到带有非对称峰的双峰型GMI曲线；当Ib为1mA时，1MHz频率下同样会出现非对称巨磁阻抗（Asymmetric GMI, AGMI）效应，且GMI效应的磁场灵敏度提升至原有水平的5.6倍。GMI效应与磁化过程受Ib诱导产生的偏置磁场显著调控，该调控机制与低且负磁致伸缩系数的富钴磁性纤维外层中具备周向易磁化轴的外层磁畴结构密切相关。在1MHz以下频率区间，仅当偏置电流超过1.5mA（此时其诱导产生的周向磁场高于14.4A/m的矫顽力）时，周向磁化与GMI效应才会受到偏置磁场的调控。当频率高于1MHz时，趋肤效应随频率升高而增强，显著降低纤维内参与周向磁化过程的总份额，进而使外层周向磁化过程对周向偏置磁场的响应更为敏感。借助偏置电流，可实现具有高磁场灵敏度的AGMI效应。