Salaheldeen Mohamed, Zhukova Valentina, Lopez Anton Ricardo, Zhukov Arcady
Department of Polymers and Advanced Materials, Faculty of Chemistry, University of the Basque Country, UPV/EHU, 20018 San Sebastian, Spain.
Department of Applied Physics I, EIG, University of the Basque Country, UPV/EHU, 20018 San Sebastian, Spain.
Sensors (Basel). 2024 Jun 6;24(11):3692. doi: 10.3390/s24113692.
We have prepared NiMnGa glass-coated microwires with different geometrical aspect ratios, = / (-diameter of metallic nucleus, and -total diameter). The structure and magnetic properties are investigated in a wide range of temperatures and magnetic fields. The XRD analysis illustrates stable microstructure in the range of from 0.25 to 0.60. The estimations of average grain size and crystalline phase content evidence a remarkable variation as the -ratio sweeps from 0.25 to 0.60. Thus, the microwires with the lowest aspect ratio, i.e., = 0.25, show the smallest average grain size and the highest crystalline phase content. This change in the microstructural properties correlates with dramatic changes in the magnetic properties. Hence, the sample with the lowest -ratio exhibits an extremely high value of the coercivity, , compared to the value for the sample with the largest -ratio (2989 Oe and 10 Oe, respectively, i.e., almost 300 times higher). In addition, a similar trend is observed for the spontaneous exchange bias phenomena, with an exchange bias field, , of 120 Oe for the sample with = 0.25 compared to a = 12.5 Oe for the sample with = 0.60. However, the thermomagnetic curves (field-cooled-FC and field-heating-FH) show similar magnetic behavior for all the samples. Meanwhile, FC and FH curves measured at low magnetic fields show negative values for = 0.25, whereas positive values are found for the other samples. The obtained results illustrate the substantial effect of the internal stresses on microstructure and magnetic properties, which leads to magnetic hardening of samples with low aspect ratio.
我们制备了具有不同几何纵横比（= / ，其中 为金属核直径， 为总直径）的NiMnGa玻璃包覆微丝。在很宽的温度和磁场范围内研究了其结构和磁性能。XRD分析表明在0.25至0.60的 范围内微观结构稳定。平均晶粒尺寸和晶相含量的估计表明，随着 比从0.25扫描到0.60，会有显著变化。因此，纵横比最低的微丝，即 = 0.25时，平均晶粒尺寸最小，晶相含量最高。微观结构性能的这种变化与磁性能的显著变化相关。因此，与纵横比最大的样品相比，纵横比最低的样品表现出极高的矫顽力 （分别为2989 Oe和10 Oe，即几乎高300倍）。此外，对于自发交换偏置现象也观察到类似趋势， = 0.25的样品的交换偏置场 为120 Oe，而 = 0.60的样品为12.5 Oe。然而，所有样品的热磁曲线（场冷-FC和场热-FH）显示出相似的磁行为。同时，在低磁场下测量的FC和FH曲线对于 = 0.25显示为负值，而其他样品为正值。所得结果说明了内应力对微观结构和磁性能的重大影响，这导致了低纵横比样品的磁硬化。
